A002954 Smallest number such that n-th iterate of Chowla function is 0.

2, 4, 8, 15, 12, 27, 24, 36, 90, 96, 245, 288, 368, 676, 1088, 2300, 1596, 1458, 3344, 3888, 5360, 8895, 11852, 25971, 23360, 38895, 35540, 35595, 36032, 53823, 47840, 62055, 59360, 83391, 70784, 128079, 145668, 349299, 254540, 327495, 293744, 328335, 167664

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn

Comments

Chowla's function (A048050) = sum of divisors of n except 1 and n.

a(83) > 10^10. - Donovan Johnson, Feb 15 2013

The first 35 terms were found by Lal and Forbes (1971). - Amiram Eldar, Mar 09 2024

References

• N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Links

• Donovan Johnson, Table of n, a(n) for n = 1..82
• M. Lal and A. Forbes, A note on Chowla's function, Math. Comp., 25 (1971), 923-925.

Crossrefs

Cf. A048050.

Programs

Mathematica

chowla[n_] := DivisorSigma[1, n] - 1 - n; chowlaSeq[n_] := Module[{m = n, cnt = 0, seq = {}}, While[m > 0 && ! MemberQ[seq, m], AppendTo[seq, m]; m = chowla[m]; cnt++]; If[m == 0, AppendTo[seq, m]]; seq]; nn = 20; t = Table[0, {nn}]; left = nn; n = 1; While[left > 0, n++; cSeq = chowlaSeq[n]; c = Length[cSeq] - 1; If[cSeq[[-1]] == 0 && c <= nn && t[[c]] == 0, t[[c]] = n; left--]]; t (* T. D. Noe, Dec 29 2011 *)

Extensions

a(31)-a(43) from T. D. Noe, Dec 29 2011