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

3, 33, 99, 135, 855, 2295, 19575, 38745, 63855, 121485, 371925, 3870195, 8109585, 28306005, 36340395, 113215095, 463084245, 672363615, 675916395, 686574735, 1208140395

Offset

1,1

Comments

Questions: Are there only multiples of 5 after the three initial terms? Are there any common terms with A228058?

Links

Table of n, a(n) for n=1..21.

Index entries for sequences where (the least) odd perfect number must occur

Index entries for sequences related to primorial base

Index entries for sequences related to sigma(n)

Prog

(PARI)
A276086(n) = { my(m=1, p=2); while(n, m *= (p^(n%p)); n = n\p; p = nextprime(1+p)); (m); };
is_A364286(n) = if(isprime(n), 0, my(u=A276086(n)); (gcd(sigma(n), u)==2*gcd(n, u))); \\ Antti Karttunen, Jul 21 2025
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, ", "))));

Crossrefs

Apart from initial 3, a subsequence of A364286.

Cf. A000203, A000396, A228058, A324198, A324644.

Cf. also A171929, A228059, A386419, A386420, A386421 for similar sequences.

Sequence in context: A123049 A153783 A048911 * A239345 A089015 A292453

Adjacent sequences: A386419 A386420 A386421 * A386423 A386424 A386425

Keyword

nonn,more

Author

Antti Karttunen, Jul 21 2025

Status

approved