A383366 Smallest of a sociable triple i < j < k such that j = s(i), k = s(j), and i = s(k), where s(k) = A380845(k) - k is the sum of aliquot divisors of k that have the same binary weight as k.

4400700, 12963816, 29878920, 38353800, 44973480, 51894304, 52208520, 67849656, 73134432, 81685080, 100711656, 103759848, 105096096, 113044896, 113161320, 114608032, 128639034, 135465912, 135559080, 136786200, 139242740, 148758120, 156686088, 159628350, 171090416

Offset: 1

Author

Amiram Eldar, Apr 24 2025

Keywords

• nonn
• base

Examples

			4400700 is a term since s(4400700) = 4840770, s(4840770) = 5456868, and s(5456868) = 4400700.
		

Links

• Amiram Eldar, Table of n, a(n) for n = 1..4400
• Amiram Eldar, Table of n, a(n), s(a(n)), s(s(a(n))) for n = 1..4400.

Crossrefs

Cf. A380845, A380846, A380849, A380850.

Programs

Mathematica

f[n_] := Module[{h = DigitCount[n, 2, 1]}, DivisorSum[n, # &, # < n && DigitCount[#, 2, 1] == h &]]; q[k_] := Module[{k1 = f[k], k2}, If[k1 <= k, False, k2 = f[k1]; k2 > k && f[k2] == k]]; Select[Range[13000000], q]

PARI

f(n) = {my(h = hammingweight(n)); sumdiv(n, d, d * (d < n && hammingweight(d) == h)); }
isok(k) = {my(k1 = f(k), k2); if(k1 <= k, 0, k2 = f(k1); k2 > k && f(k2) == k);}