A154820 Numbers whose trajectory under iteration of sum of cubes of digits eventually turns out to follow the cyclic iteration of 133, 55, 250.

4, 13, 25, 28, 31, 40, 46, 52, 55, 64, 82, 103, 130, 133, 205, 208, 250, 256, 265, 280, 289, 298, 301, 310, 313, 331, 349, 394, 400, 406, 439, 448, 460, 484, 493, 502, 505, 520, 526, 550, 562, 589, 598, 604, 625, 640, 652, 679, 697, 769, 796, 802, 820, 829

Offset

1,1

Comments

All the numbers are of the form 3n+1.

Subsequence of A165336. - Reinhard Zumkeller, Sep 17 2009

Links

Table of n, a(n) for n=1..54.

Example

Taking 40 for example,
  4^3 + 0^3 = 64;
  6^3 + 4^3 = 280;
  2^3 + 8^3 + 0^3 = 520;
  5^3 + 2^3 + 0^3 = 133;
  1^3 + 3^3 + 3^3 = 55;
  5^3 + 5^3 = 250.

Maple

A055012 := proc(n) local a, d ; a := 0 ; for d in convert(n, base, 10) do a := a+d^3; od; a ; end: isA154820 := proc(n) local traj, t ; t := n ; traj := {} ; while true do if t in traj then if t in {133, 55, 250} then RETURN(true) ; else RETURN(false) ; fi; else traj := traj union {t} ; t := A055012(t) ; fi; od: end: for n from 1 to 1000 do if isA154820(n) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Jan 18 2009

Crossrefs

Cf. A165337, A154877, A165336, A165339.

Sequence in context: A272702 A272734 A273414 * A056708 A307271 A333297

Adjacent sequences: A154817 A154818 A154819 * A154821 A154822 A154823

Keyword

nonn,base

Author

Avik Roy (avik_3.1416(AT)yahoo.co.in), Jan 15 2009

Extensions

Extended by R. J. Mathar, Jan 18 2009

Edited by Charles R Greathouse IV, Aug 02 2010

Status

approved