A046930 Size of sea of composite numbers surrounding n-th prime.

1, 1, 2, 4, 4, 4, 4, 4, 8, 6, 6, 8, 4, 4, 8, 10, 6, 6, 8, 4, 6, 8, 8, 12, 10, 4, 4, 4, 4, 16, 16, 8, 6, 10, 10, 6, 10, 8, 8, 10, 6, 10, 10, 4, 4, 12, 22, 14, 4, 4, 8, 6, 10, 14, 10, 10, 6, 6, 8, 4, 10, 22, 16, 4, 4, 16, 18, 14, 10, 4, 8, 12, 12, 10, 8, 8, 12, 10, 10, 16, 10, 10, 10, 6, 8, 8

Offset

1,3

Links

T. D. Noe, Table of n, a(n) for n = 1..10000

Formula

a(n) = A031131(n) - 2 for n > 1. - Reinhard Zumkeller, Dec 19 2013

Example

23 is in a sea of 8 composites: 20,21,22,23,24,25,26,27,28.

Maple

[ seq(ithprime(i)-ithprime(i-2)-2, i=3..100) ];

Mathematica

Table[ Prime[n + 2] - Prime[n] - 2, {n, 75}] (* Robert G. Wilson v Oct 27 2004 *)
Join[{1}, #[[3]]-#[[1]]-2&/@Partition[Prime[Range[90]], 3, 1]] (* Harvey P. Dale, Sep 26 2012 *)

Prog

(Haskell)
a046930 1 = 1
a046930 n = subtract 2 $ a031131 n  -- Reinhard Zumkeller, Dec 19 2013

Crossrefs

Related sequences: A023186-A023188, A046929-A046931, A051650, A051652, A051697-A051702, A051728-A051730.

Sequence in context: A287393 A260085 A159461 * A302254 A160409 A035645

Adjacent sequences: A046927 A046928 A046929 * A046931 A046932 A046933

Keyword

nonn,easy,nice

Author

N. J. A. Sloane, Marc LeBrun

Extensions

More terms from Michel ten Voorde

Status

approved