A179288 a(n) is the smallest prime number p that makes both 2p + prime(n) and p + 2*prime(n) prime numbers.

5, 3, 3, 31, 3, 3, 5, 7, 139, 5, 5, 19, 23, 3, 3, 19, 5, 3, 139, 3, 5, 7, 19, 3, 31, 5, 37, 11, 7, 23, 31, 7, 5, 61, 11, 3, 5, 3, 3, 31, 5, 19, 3, 7, 41, 11, 3, 3, 5, 37, 79, 5, 61, 7, 37, 19, 5, 3, 79, 5, 7, 3, 19, 17, 7, 11, 53, 127, 41, 3, 109, 17, 5, 11, 3, 79, 17, 19, 5, 19, 11, 151, 17, 5, 67, 79, 5, 19, 107, 37, 61, 17, 109, 11, 3, 31, 61, 17, 11, 23

Offset

2,1

Links

Zak Seidov, Table of n, a(n) for n = 2..1001

Example

For n=2, prime(n)=3, and a(n)=5 because 2x3+5=11 and 3+2x5=13 are prime;
For n=3, prime(n)=5, and a(n)=3 because 2x5+3=13 and 5+2x3=11 are prime;
...
for n=9, prime(n)=23, and a(n)=7 because 2*23+7=53 and 23+2*7=37 are prime.

Mathematica

f[n_] := Block[{i = 2, p = Prime[n + 1]}, While[q = Prime[i]; !PrimeQ[2 p + q] || !PrimeQ[p + 2 q], i++]; q]; Array[f, 60] (* Robert G. Wilson v, based on Lei Zhou's program, Jan 05 2011 *)

Crossrefs

Sequence in context: A276759 A079799 A257378 * A021871 A309611 A348434

Adjacent sequences: A179285 A179286 A179287 * A179289 A179290 A179291

Keyword

nonn,easy

Author

Lei Zhou, Jan 05 2011

Status

approved