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.

A342630 Numbers k such that A340180(k) is prime.

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%I A342630 #7 Mar 18 2021 22:59:20
%S A342630 5,6,7,14,18,24,29,34,39,41,47,53,77,114,119,148,150,159,176,188,189,
%T A342630 190,191,205,215,217,218,241,268,288,312,314,331,334,339,342,346,352,
%U A342630 364,367,387,390,402,418,429,438,439,440,446,449,480,493,494,500,504,510,521,523,546,549,553,561,580
%N A342630 Numbers k such that A340180(k) is prime.
%H A342630 Robert Israel, <a href="/A342630/b342630.txt">Table of n, a(n) for n = 1..5000</a>
%e A342630 a(4) = 14 is a term because A340180(14) = 23 is prime.
%p A342630 f:= proc(n) local s,k;
%p A342630   s:= numtheory:-sigma(n);
%p A342630   add(`if`(igcd(n,k)=1, s mod k, 0),k=1..n-1);
%p A342630 end proc:
%p A342630 select(t -> isprime(f(t)), [$1..1000]);
%Y A342630 Cf. A340180.
%K A342630 nonn
%O A342630 1,1
%A A342630 _J. M. Bergot_ and _Robert Israel_, Mar 17 2021