cp's OEIS Frontend

This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.

A349110 Powerful numbers (A001694) whose sum of aliquot powerful divisors (including 1) is larger than 1 and is also powerful.

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%I A349110 #7 Nov 08 2021 04:29:05
%S A349110 128,729,900,4900,10404,17424,24336,52900,78400,79524,81796,297025,
%T A349110 304175,304200,313600,346921,417316,532900,1612900,1656200,1960000,
%U A349110 2238016,2464900,3129361,3232804,3334276,3496900,3534400,3992004,6056521,6974881,9245000,10672200
%N A349110 Powerful numbers (A001694) whose sum of aliquot powerful divisors (including 1) is larger than 1 and is also powerful.
%C A349110 Numbers k such that A112526(k) = A112526(A183097(k) - k) = 1.
%e A349110 128 = 2^7 is a term since it is powerful and the sum of its aliquot powerful divisors, A183097(128) - 128 =  1 + 4 + 8 + 16 + 32 + 64 = 125 = 5^3 is also powerful.
%t A349110 powQ[n_] := AllTrue[FactorInteger[n][[;;,2]], # > 1 &]; f[p_, e_] := (p^(e + 1) - 1)/(p - 1) - p; s[1] = 1; s[n_] := Times @@ f @@@ FactorInteger[n]; q[n_] := powQ[n] && powQ[s[n] - n]; Select[Range[1.1*10^7], q]
%o A349110 (PARI) isok(n) = my(s); ispowerful(n) && (s=sumdiv(n, d, if (d<n, d*ispowerful(d)))) && (s>1) && ispowerful(s); \\ _Michel Marcus_, Nov 08 2021
%Y A349110 Cf. A001694, A183097, A349109.
%K A349110 nonn
%O A349110 1,1
%A A349110 _Amiram Eldar_, Nov 08 2021