A364256 a(n) = gcd(n, A243071(n)).

1, 1, 3, 2, 1, 6, 1, 4, 1, 2, 1, 12, 1, 2, 1, 8, 1, 2, 1, 4, 1, 2, 1, 24, 1, 2, 9, 4, 1, 2, 1, 16, 1, 2, 1, 4, 1, 2, 1, 8, 1, 2, 43, 4, 5, 2, 1, 48, 1, 2, 1, 4, 1, 18, 1, 8, 1, 2, 1, 4, 1, 2, 3, 32, 1, 2, 1, 4, 1, 2, 1, 8, 1, 2, 3, 4, 11, 2, 1, 16, 1, 2, 1, 4, 1, 86, 1, 8, 1, 10, 7, 4, 1, 2, 1, 96, 1, 2, 11, 4

Offset: 1

Author

Antti Karttunen, Jul 17 2023

Keywords

• nonn

Comments

Primes p such that a(p) = p are those that occur as factors of (2^A000720(p))-1: 3, 43, 49477. Are there any more of them?

Links

• Antti Karttunen, Table of n, a(n) for n = 1..16384
• Index entries for sequences computed from indices in prime factorization

Crossrefs

Cf. A243071.

Cf. also A364254, A364255.

Programs

PARI

A064989(n) = {my(f); f = factor(n); if((n>1 && f[1,1]==2), f[1,2] = 0); for (i=1, #f~, f[i,1] = precprime(f[i,1]-1)); factorback(f)};
A243071(n) = if(n<=2, n-1, if(!(n%2), 2*A243071(n/2), 1+(2*A243071(A064989(n)))));
A364256(n) = gcd(n, A243071(n));