easy iteration generates polynomial sequences
  1. Definition
  K-sequence is defined as follows, K is for "kimyo" which means strange in Japanese :
 
     x(n)=[a*x(n-1)+b]/p^r,  a, b are real number, [x] is integer part of x,
                 p is prime, p^r is the highest power of p dividing [a*x(n-1)+b]
 
  2. Collatz's sequence
  This is a generalization of Collatz's 3x+1 sequence.
  Because, K-sequence is the iteration of f(x)=[a*x+b]/p^r, and if p=2 and a=1.5*2^s and b=0.5*2^s+c, 0<=s, 0<=c<1
  then f(x)=[1.5*2^s*x+0.5*2^s+c]/2^r
        =(1.5*2^s*x+0.5*2^s)/2^r
        =(3*x+1)/2^(r-s+1)
  It becomes the definition of Collatz's sequence.
  But for example 3,10,5,16,8,4,2,1,4,2,1,--- is represented more compactly as     3,5,1,1,1,1,1--- .
 
  3. many polynomial subsequences.   Records
  LLI, an abrreviation of "a lot of linear parts which are isolated each other", is defined as follows :
 
     K-sequence such that p=2, a=2+e, 0<e<k, k is about 0.01
 
  Indeed, on LLI { x0,p,a,b=1,2,2.00013,3.0 }, between 0-th term and 10000-th term, there are 44 linear subsequences such that 4<={number of terms}.
  The first several are :
     x(16) to x(3613)     x(n)=x(n-1)+2
     x(3650) to x(3655)   x(n)=x(n-1)+1028
     x(3820) to x(3848)   x(n)=x(n-1)+66
     ..........
  From a linear part to next linear part, LLI behaves as if it were a random sequence.
 
  Besides them, LLI has second degree's parts, and third and fourth degree's parts.
 
  ex. 2nd.
  LLI { x0, p, a, b = 2443499297,2,2.00014,3.0 } :
  the 68 terms from 0-th to 67-th are represented as follows.
  x(n) = 6*n^2+171040*n+2443499297
  
  ex. 3rd.
   LLI { x0,p,a,b=2417903893829791,2,2.00013,3.0 } :
  the 5 terms from 0-th term to 4-th term are represented as follows.
  x(n) = 664/6*n^3+5107490*n^2+471475936498/3*n+2417903893829791
 
  ex. 4th
  LLI { x0,p,a,b=2015985557869547951,2,2.00013,3.2 }  
  a subsequence of 4th degree exists, from 0-th term to 7-th term.
  2015985557869547951 2016116596930809473 2016247644509609977
  2016378700606503103 2016509765222042527 2016640838356781961
  2016771920011275153 2016903010186075887 
 
    Examples of LLI.
                 x0,p,a,b=1,2,2.00001,3.0    period=180492
                 x0,p,a,b=1,2,2.00013,3.2    period=6366
                 x0,p,a,b=1,2,2.00013,3.0    period=1790641
                 x0,p,a,b=1,2,2.0001,3.0     period=13677
                 x0,p,a,b=1,2,2.001,3.2     period=1670
                 x0,p,a,b=1,2,2.001,3.0     period=11078
                 x0,p,a,b=12345,2,2.001,2.8   period=11048
                 x0,p,a,b=1,2,2.00001,3.2     period unknown
                 x0,p,a,b=1,2,2.00014,3.0     period=73667
                 x0,p,a,b=10^50+1,2,2.001,3.2   period unknown
 
 
  4. several classes of K-sequences
  o ESS, for extremely strange sequence, is defined as follows :
 
     K-sequence such that a=p^r+e , 0<e<k , k is about 0.01.
     the case of p=2, r=1 is LLI.
 
   ESS looks like a mosaic of periodic subsequences and linear subsequences and random behaving subsequence.
   Only LLI is different from the other ESS.
   For example, ESS, x0,p,a,b=1,2,4.001, 1.2 is similar to ESS, x0,p,a,b=1,3,3.00001,1.2 , but is absolutely different to LLI.
 
  o Another class : x0=3, p=2, a=1.6, 1.0<b<=1.2
   These sequences seem to be unbounded.
   The period of K-sequence such that x0,p,a,b=107,2,1.6,1.1 is still unknown
       Don Reble calculated x(2,000,000) = 852756...564079; it has 46892digits.
 
  5. a program for K-sequence in Mathematica
  In[1]:=
  g[x_] := If[Mod[Floor[a*x + b], p] == 0,
     Floor[a*x + b]/p^IntegerExponent[Floor[a*x + b], p], Floor[a*x + b]];
  In[2]:=
  a = 5.0001; b = 1.0; p = 5;
  NestList[g, 1, 200]
  Out[3]=
{1, 6, 31, 156, 781, 3906, 19531, 97657, 97659, 97661, 97663, 19533, 97667, \
97669, 97671, 97673, 3907, 19536, 97682, 97684, 97686, 97688, 19538, 97692,\
97694, 97696, 97698, 3908, 19541, 97707, 97709, 97711, 97713, 19543, 97717,\
97719, 97721, 97723, 3909, 19546, 97732, 97734, 97736, 97738, 19548, 97742,\
97744, 97746, 97748, 782, 3911, 19556, 97782, 97784, 97786, 97788, 19558, \
97792, 97794, 97796, 97798, 3912, 19561, 97807, 97809, 97811, 97813, 19563, \
97817, 97819, 97821, 97823, 3913, 19566, 97832, 97834, 97836, 97838, 19568, \
97842, 97844, 97846, 97848, 3914, 19571, 97857, 97859, 97861, 97863, 19573, \
97867, 97869, 97871, 97873, 783, 3916, 19581, 97907, 97909, 97911, 97913, \
19583, 97917, 97919, 97921, 97923, 3917, 19586, 97932, 97934, 97936, 97938, \
19588, 97942, 97944, 97946, 97948, 3918, 19591, 97957, 97959, 97961, 97963, \
19593, 97967, 97969, 97971, 97973, 3919, 19596, 97982, 97984, 97986, 97988, \
19598, 97992, 97994, 97996, 97998, 784, 3921, 19606, 98032, 98034, 98036, \
98038, 19608, 98042, 98044, 98046, 98048, 3922, 19611, 98057, 98059, 98061, \
98063, 19613, 98067, 98069, 98071, 98073, 3923, 19616, 98082, 98084, 98086, \
98088, 19618, 98092, 98094, 98096, 98098, 3924, 19621, 98107, 98109, 98111, \
98113, 19623, 98117, 98119, 98121, 98123, 157, 786, 3931, 19656, 98282, \
98284, 98286, 98288, 19658, 98292, 98294, 98296, 98298, 3932, 19661, 98307, \
98309}
 
  6. open problems
     1. Why such an easy iteration generates many polynomial subsequences?
     2. Find the periods of sequences whose periods are not known.
 
  7. a conjecture
     " For any n, an LLI which has n-th degree polynomial sequences exists. "
 
  All mathematicians, please study about this strange sequence !!
 
  Neil Sloane once said, "Indeed, it is strange."
  Eric Roosentaal said, "There are a few ways to generalize Collats, but Ithink you have taken the broadest definition possible."
  Another mathematician said, " He found all kinds of weird sequences. "
 
  Three examples of K-sequence are mentioned on On-line Encyclopedia of Integer Sequences.
  A028948, A029580, A036982
 
  a graph of the first 1000 terms of ESS { x0,p,a,b = 1,2,4.001,1.2 } first line represents 0 to 500, and second line represents 501 to 1000. It behaves cyclic like -> chaotic -> linear -> random * exponetial.  
  Yasutoshi