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 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
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS All the numbers are of the form 3n+1. Subsequence of A165336. - Reinhard Zumkeller, Sep 17 2009 LINKS 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 A092484 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

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Last modified January 26 20:33 EST 2020. Contains 331288 sequences. (Running on oeis4.)