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.

A335196 Nonunitary admirable numbers: numbers k such that there is a nonunitary divisor d of k such that nusigma(k) - 2*d = k, where nusigma is the sum of nonunitary divisors function (A048146).

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%I A335196 #12 Apr 04 2023 07:43:26
%S A335196 48,80,96,108,120,160,168,180,192,216,224,252,264,280,300,312,320,336,
%T A335196 352,360,384,396,408,416,432,448,456,468,480,504,528,540,552,560,600,
%U A335196 612,624,640,672,684,696,704,720,744,756,768,792,816,828,832,840,864,880
%N A335196 Nonunitary admirable numbers: numbers k such that there is a nonunitary divisor d of k such that nusigma(k) - 2*d = k, where nusigma is the sum of nonunitary divisors function (A048146).
%C A335196 Equivalently, numbers that are equal to the sum of their nonunitary divisors, with one of them taken with a minus sign.
%H A335196 Amiram Eldar, <a href="/A335196/b335196.txt">Table of n, a(n) for n = 1..10000</a>
%e A335196 48 is a term since 48 = 2 - 4 + 6 + 8 + 12 + 24 is the sum of its nonunitary divisors with one of them, 4, taken with a minus sign.
%t A335196 usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); nusigma[n_] := DivisorSigma[1, n] - usigma[n]; nuAdmQ[n_] := (ab = nusigma[n] - n) > 0 && EvenQ[ab] && ab/2 < n && !CoprimeQ[ab/2, 2*n/ab]; Select[Range[1000], nuAdmQ]
%Y A335196 The nonunitary version of A111592.
%Y A335196 Subsequence of A064597.
%Y A335196 Similar sequences: A328328, A334972, A334974.
%Y A335196 Cf. A048146.
%K A335196 nonn
%O A335196 1,1
%A A335196 _Amiram Eldar_, May 26 2020