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A046930
Size of sea of composite numbers surrounding n-th prime.
7
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
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
KEYWORD
nonn,easy,nice
EXTENSIONS
More terms from Michel ten Voorde
STATUS
approved