A072918 a(n) = p(n) - sigma(n), where p(n) is the least prime greater than sigma(n).

1, 2, 1, 4, 1, 1, 3, 2, 4, 1, 1, 1, 3, 5, 5, 6, 1, 2, 3, 1, 5, 1, 5, 1, 6, 1, 1, 3, 1, 1, 5, 4, 5, 5, 5, 6, 3, 1, 3, 7, 1, 1, 3, 5, 1, 1, 5, 3, 2, 4, 1, 3, 5, 7, 1, 7, 3, 7, 1, 5, 5, 1, 3, 4, 5, 5, 3, 1, 1, 5, 1, 2, 5, 13, 3, 9, 1, 5, 3, 5, 6, 1, 5, 3, 1, 5, 7, 1, 7, 5, 1, 5, 3, 5, 7, 5, 3, 2, 1, 6

Offset

1,2

Links

Antti Karttunen, Table of n, a(n) for n = 1..16384

Formula

a(n) = A013632(A000203(n)). - Antti Karttunen, Nov 07 2017

Example

phi(4) = 7 and the least prime > 7 is 11; hence a(4) = 11 - 7 = 4.

Mathematica

ps[n_]:=Module[{sn=DivisorSigma[1, n]}, NextPrime[sn]-sn]; ps/@Range[100] (* Harvey P. Dale, Feb 02 2011 *)

Prog

(PARI) A072918(n) = (nextprime(1+sigma(n)) - sigma(n)); \\ Antti Karttunen, Nov 07 2017

Crossrefs

Cf. A000203, A013632, A202111.

Sequence in context: A072341 A011130 A291854 * A255878 A162944 A140582

Adjacent sequences: A072915 A072916 A072917 * A072919 A072920 A072921

Keyword

easy,nonn

Author

Joseph L. Pe, Aug 11 2002

Status

approved