A020549 -id:A020549 - cp's OEIS frontend

A306507 a(n) = gcd(n!^2+1, sigma(n!)), where sigma() denotes the sum of the divisors.

1, 1, 1, 1, 1, 13, 1, 17, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 61, 1, 1, 1, 1, 1, 1, 1, 1, 61, 1, 1, 1, 193, 1, 1, 1, 757, 61, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 109, 1, 1, 1, 181, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 113

Offset: 1

Graph
List
Refs
Listen
History
Text
Internal format

Daoudi Rédoane, Feb 20 2019

nonn

A sequence that produces primes.
A counterexample is found at n=7880, here the gcd is 380927609 = 15761*24169.
Interesting properties may be found in this sequence, for example many primes are 2n+1.

Cf. A000203, A020549, A062569.

Table[GCD[(n!)^2+1,DivisorSigma[1,n!]],{n,90}] (* Harvey P. Dale, Jun 03 2021 *)

a(n) = gcd(n!^2+1, sigma(n!)); \\ Michel Marcus, Feb 20 2019

a(n) = gcd(A020549(n), A062569(n)).

More terms from Michel Marcus, Feb 20 2019

cp's OEIS Frontend

A306507 a(n) = gcd(n!^2+1, sigma(n!)), where sigma() denotes the sum of the divisors.

Views

Author

Keywords

Comments

Crossrefs

Programs

Mathematica

PARI

Formula

Extensions