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A352264 Integers that need 6 iterations of the map x->A352172(x) to reach 1. 8
377, 737, 773, 1377, 1737, 1773, 3077, 3177, 3707, 3717, 3770, 3771, 3889, 3898, 3988, 4689, 4698, 4869, 4896, 4968, 4986, 5677, 5767, 5776, 6489, 6498, 6577, 6668, 6686, 6757, 6775, 6849, 6866, 6894, 6948, 6984, 7037, 7073, 7137, 7173, 7307, 7317, 7370, 7371, 7567, 7576 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
EXAMPLE
377 -> 3176523 -> 54010152000 -> 8000000 -> 512 -> 1000 -> 1.
MATHEMATICA
f[n_] := (Times @@ Select[IntegerDigits[n], # > 1 &])^3; q[n_, len_] := (v = Nest[f, n, len - 1]) != 1 && f[v] == 1; Select[Range[7576], q[#, 6] &] (* Amiram Eldar, Mar 10 2022 *)
PROG
(PARI) f(n) = vecprod(apply(x->x^3, select(x->(x>1), digits(n)))); \\ A352172
isok6(n) = {for (k=1, 6, n = f(n); if ((n==1), return(k==6)); ); }
(Python)
from math import prod
def A352172(n): return prod(int(d)**3 for d in str(n) if d != '0')
def ok(x, iters=6):
i = 0
while i < iters and x != 1: i, x = i+1, A352172(x)
return i == iters and x == 1
print([k for k in range(7577) if ok(k)]) # Michael S. Branicky, Mar 10 2022
CROSSREFS
Cf. A352172. Subsequence of A351876.
Sequence in context: A198640 A171489 A105717 * A222350 A277942 A241908
KEYWORD
nonn,base
AUTHOR
Michel Marcus, Mar 10 2022
STATUS
approved

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Last modified April 22 17:45 EDT 2024. Contains 371906 sequences. (Running on oeis4.)