A175191 a(n) = the smallest positive integer such that (the n-th prime)+2*a(n) is composite.

1, 3, 2, 1, 2, 1, 2, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 2, 1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 1, 1, 2, 1, 1, 1, 1, 1, 2, 1

Offset

1,2

Comments

Every term except a(2) (which is 3) is either 1 or 2.

Links

G. C. Greubel, Table of n, a(n) for n = 1..1000

Maple

a:= n-> `if`(n=2, 3, `if`(isprime(ithprime(n)+2), 2, 1)):
seq(a(n), n=1..105);  # Alois P. Heinz, Oct 02 2020

Mathematica

spi[n_]:=Module[{i=1}, While[PrimeQ[Prime[n]+2i], i++]; i]; Array[spi, 110] (* Harvey P. Dale, Apr 23 2012 *)

Crossrefs

Sequence in context: A181715 A077089 A156352 * A328928 A342468 A324534

Adjacent sequences: A175188 A175189 A175190 * A175192 A175193 A175194

Keyword

nonn

Author

Leroy Quet, Mar 01 2010

Extensions

Extended by Ray Chandler, Mar 04 2010

Status

approved