A325976 a(n) is the largest k <= n such that k and (2n-sigma(n)) [= A033879(n)] are relatively prime.

1, 2, 3, 4, 5, 1, 7, 8, 9, 9, 11, 11, 13, 13, 13, 16, 17, 17, 19, 19, 21, 21, 23, 23, 25, 23, 27, 1, 29, 29, 31, 32, 31, 33, 35, 36, 37, 37, 39, 39, 41, 41, 43, 43, 43, 43, 47, 47, 49, 50, 49, 49, 53, 53, 55, 55, 57, 57, 59, 59, 61, 61, 63, 64, 65, 65, 67, 67, 67, 69, 71, 71, 73, 73, 75, 73, 77, 77, 79, 79, 81, 81, 83, 83, 85, 83

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..16385

Antti Karttunen, Data supplement: n, a(n) computed for n = 1..65537

Index entries for sequences related to sigma(n)

Formula

a(n) = n - A325817(n) = A033879(n) + A325826(n).

a(n) >= A325959(n).

gcd(a(n), A325826(n)) = 1.

Prog

(PARI) A325976(n) = { my(s=sigma(n)); forstep(k=n, 0, -1, if(1==gcd((n+n-s), k), return(k))); };
(PARI)
A325817(n) = { my(s=sigma(n)); for(i=0, s, if(1==gcd(n-i, n-(s-i)), return(i))); };
A325976(n) = (n - A325817(n));

Crossrefs

Cf. A033879, A325817, A325818, A325826, A325959.

Sequence in context: A253247 A201059 A325959 * A319654 A244414 A214394

Adjacent sequences: A325973 A325974 A325975 * A325977 A325978 A325979

Keyword

nonn

Author

Antti Karttunen, Jun 01 2019

Status

approved