A380849 -id:A380849 - cp's OEIS frontend

A380850 Greater of a pair of amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A380845(k) - k is the sum of aliquot divisors of k that have the same binary weight as k.

36068, 145124, 153670, 294075, 290532, 581348, 593100, 1099530, 2066625, 1237830, 2326244, 2338832, 2476870, 6393390, 4652772, 4883976, 6854625, 9279675, 9548325, 6514464, 11725857, 8760548, 9237668, 9305828, 9457356, 8717912, 12190132, 12353716, 10607740, 12493444

Offset: 1

Amiram Eldar, Feb 06 2025

Analogous to amicable numbers (A002025 and A002046) with A380845 instead of A000203.

The terms are ordered according to their lesser counterparts (A380849).

			36068 is a term since A380845(36068) - 36068 = 27940 < 36068 and A380845(27940) - 27940 = 36068.

Amiram Eldar, Table of n, a(n) for n = 1..12000

Cf. A000203, A002025, A002046, A380845, A380846, A380849.

f[n_] := Module[{h = DigitCount[n, 2, 1]}, DivisorSum[n, # &, # < n && DigitCount[#, 2, 1] == h &]];
seq[lim_] := Module[{s = {}, m}, Do[m = f[n]; If[m > n && f[m] == n, AppendTo[s, m]], {n, 1, lim}]; s]; seq[10^6]

f(n) = {my(h = hammingweight(n)); sumdiv(n, d, d * (d < n && hammingweight(d) == h));}
list(lim) = {my(m); for(n = 1, lim, m = f(n); if(m > n && f(m) == n, print1(m, ", ")));}

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.

Original entry on oeis.org

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

Amiram Eldar, Apr 24 2025

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

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.

Cf. A380845, A380846, A380849, A380850.

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]

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);}

cp's OEIS Frontend

A380850 Greater of a pair of amicable numbers k < m such that s(k) = m and s(m) = k, where s(k) = A380845(k) - k is the sum of aliquot divisors of k that have the same binary weight as k.

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