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.

A323331 Smallest member of sociable quadruples using Dedekind psi function (A001615).

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%I A323331 #7 Jan 11 2019 04:23:32
%S A323331 11398670,22797340,38369450,45594680,56993350,59334310,76738900,
%T A323331 91189360,113986700,118668620,153477800,182378720,209524210,227973400,
%U A323331 237337240,268586150,284966750,306955600,364757440,419048420,455946800,474674480,537172300,539867650,569933500
%N A323331 Smallest member of sociable quadruples using Dedekind psi function (A001615).
%C A323331 Numbers k whose iterations of k -> A001615(k) - k are cyclic with a period of 4, and in each cyclic quadruple k is the least of the 4 members.
%e A323331 11398670 is in the sequence since the iterations of k -> A001615(k) - k are cyclic with a period of 4: 11398670, 11475730, 12474350, 14093650, 11398670, ... and 11398670 is the smallest member of the quadruple.
%t A323331 t[0]=0; t[1]=0; t[n_]:=(Times@@(1+1/Transpose[FactorInteger[n]][[1]])-1)*n;
%t A323331 seq[n_]:=NestList [t, n, 4][[2;; 5]] ; aQ[n_] := Module[ {s=seq[n]}, n==Min[s] && Count[s, n]==1]; s={}; Do[If[aQ[n], AppendTo[s, n]], {n, 1, 10^9}]; s
%Y A323331 Cf. A001615, A090615, A319902, A319915, A323327, A323328, A323329, A323330.
%K A323331 nonn
%O A323331 1,1
%A A323331 _Amiram Eldar_, Jan 11 2019