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.

%I A380850 #9 Feb 07 2025 00:44:41
%S A380850 36068,145124,153670,294075,290532,581348,593100,1099530,2066625,
%T A380850 1237830,2326244,2338832,2476870,6393390,4652772,4883976,6854625,
%U A380850 9279675,9548325,6514464,11725857,8760548,9237668,9305828,9457356,8717912,12190132,12353716,10607740,12493444
%N 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.
%C A380850 Analogous to amicable numbers (A002025 and A002046) with A380845 instead of A000203.
%C A380850 The terms are ordered according to their lesser counterparts (A380849).
%H A380850 Amiram Eldar, <a href="/A380850/b380850.txt">Table of n, a(n) for n = 1..12000</a>
%e A380850 36068 is a term since A380845(36068) - 36068 = 27940 < 36068 and A380845(27940) - 27940 = 36068.
%t A380850 f[n_] := Module[{h = DigitCount[n, 2, 1]}, DivisorSum[n, # &, # < n && DigitCount[#, 2, 1] == h &]];
%t A380850 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]
%o A380850 (PARI) f(n) = {my(h = hammingweight(n)); sumdiv(n, d, d * (d < n && hammingweight(d) == h));}
%o A380850 list(lim) = {my(m); for(n = 1, lim, m = f(n); if(m > n && f(m) == n, print1(m, ", ")));}
%Y A380850 Cf. A000203, A002025, A002046, A380845, A380846, A380849.
%K A380850 nonn,base
%O A380850 1,1
%A A380850 _Amiram Eldar_, Feb 06 2025