A325971 a(n) is the least k >= A007947(n) such that -n + k and (n-sigma(n))+k are relatively prime.

1, 2, 4, 2, 6, 7, 8, 2, 3, 11, 12, 7, 14, 15, 16, 2, 18, 7, 20, 11, 22, 23, 24, 7, 5, 27, 4, 27, 30, 31, 32, 2, 34, 35, 36, 6, 38, 39, 40, 11, 42, 43, 44, 23, 16, 47, 48, 7, 7, 10, 52, 27, 54, 7, 56, 15, 58, 59, 60, 31, 62, 63, 22, 2, 66, 67, 68, 35, 70, 71, 72, 7, 74, 75, 16, 39, 78, 79, 80, 11, 3, 83, 84, 43, 86, 87, 88, 23, 90, 31

Offset

1,2

Comments

a(n) is the least k >= A007947(n) such that n-k and n-(sigma(n)-k) are relatively prime.

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) - A325972(n).

a(n) = n - A325970(n).

Prog

(PARI)
A007947(n) = factorback(factorint(n)[, 1]); \\ From A007947
A325971(n) = { my(s=sigma(n)); for(i=A007947(n), s, if(1==gcd(n-i, n-(s-i)), return(i))); (0); };
A325971(n) = { my(s=sigma(n)); for(k=A007947(n), s, if(1==gcd(-n + k, (n-sigma(n))+k), return(k))); };

Crossrefs

Cf. A000203, A007947, A324213, A325817, A325961, A325965, A325970, A325972.

Sequence in context: A216369 A083791 A303347 * A250222 A026251 A205721

Adjacent sequences: A325968 A325969 A325970 * A325972 A325973 A325974

Keyword

nonn

Author

Antti Karttunen, May 31 2019

Status

approved