cp's OEIS Frontend

A386422 Odd numbers k that are closer to being perfect than previous terms and also satisfy the condition that A324644(k)/A324198(k) = 2.

%I A386422 #8 Jul 21 2025 13:13:10
%S A386422 3,33,99,135,855,2295,19575,38745,63855,121485,371925,3870195,8109585,
%T A386422 28306005,36340395,113215095,463084245,672363615,675916395,686574735,
%U A386422 1208140395
%N A386422 Odd numbers k that are closer to being perfect than previous terms and also satisfy the condition that A324644(k)/A324198(k) = 2.
%C A386422 Questions: Are there only multiples of 5 after the three initial terms? Are there any common terms with A228058?
%H A386422 <a href="/index/O#opnseqs">Index entries for sequences where (the least) odd perfect number must occur</a>
%H A386422 <a href="/index/Pri#primorialbase">Index entries for sequences related to primorial base</a>
%H A386422 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%o A386422 (PARI)
%o A386422 A276086(n) = { my(m=1, p=2); while(n, m *= (p^(n%p)); n = n\p; p = nextprime(1+p)); (m); };
%o A386422 is_A364286(n) = if(isprime(n), 0, my(u=A276086(n)); (gcd(sigma(n),u)==2*gcd(n,u))); \\ _Antti Karttunen_, Jul 21 2025
%o A386422 m=-1; n=-1; k=0; while(m!=0, n+=2; if(!((n-1)%(2^25)),print1("("n")")); if(isprime(n) || is_A364286(n), if((m<0) || abs((sigma(n)/n)-2)<m, m=abs((sigma(n)/n)-2); k++; write("b386422.txt", k, " ", n); print1(n, ", "))));
%Y A386422 Apart from initial 3, a subsequence of A364286.
%Y A386422 Cf. A000203, A000396, A228058, A324198, A324644.
%Y A386422 Cf. also A171929, A228059, A386419, A386420, A386421 for similar sequences.
%K A386422 nonn,more
%O A386422 1,1
%A A386422 _Antti Karttunen_, Jul 21 2025