A325965 a(n) is the least k >= A020639(n) such that n-k and n-(sigma(n)-k) are relatively prime.

1, 2, 4, 2, 6, 5, 8, 2, 3, 3, 12, 3, 14, 3, 4, 2, 18, 2, 20, 3, 4, 3, 24, 5, 5, 3, 4, 27, 30, 5, 32, 2, 4, 3, 6, 2, 38, 3, 4, 3, 42, 5, 44, 3, 4, 3, 48, 3, 7, 2, 4, 3, 54, 5, 6, 3, 4, 3, 60, 5, 62, 3, 4, 2, 6, 5, 68, 5, 4, 3, 72, 2, 74, 3, 4, 3, 8, 5, 80, 3, 3, 3, 84, 3, 6, 3, 4, 3, 90, 5, 8, 3, 4, 3, 6, 5, 98, 2, 4, 2

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..20000

Index entries for sequences related to sigma(n)

Formula

a(n) = A000203(n) - A325966(n).

For all n:

a(A000396(n)) = A000396(n)-1.

a(n) >= A325817(n).

Prog

(PARI)
A020639(n) = if(1==n, n, factor(n)[1, 1]);
A325965(n) = { my(s=sigma(n)); for(i=A020639(n), s, if(1==gcd(n-i, n-(s-i)), return(i))); };

Crossrefs

Cf. A000203, A000396, A020639, A325817, A325966.

Sequence in context: A049200 A347100 A164701 * A198540 A216369 A083791

Adjacent sequences: A325962 A325963 A325964 * A325966 A325967 A325968

Keyword

nonn

Author

Antti Karttunen, May 29 2019

Status

approved