OFFSET
1,1
COMMENTS
Obviously a(n) is odd or even as n is even or odd.
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
a(4) = 9 as (9-1)/4 = 2 and 9*4 + 1 = 37 both are primes.
a(9) = 64, (64-1)/9 = 7 and 64*9 + 1 = 577 both are primes.
MATHEMATICA
bp[n_]:=Module[{k=2n+1}, While[!PrimeQ[(k-1)/n]||!PrimeQ[k*n+1], k++]; k]; Array[bp, 60] (* Harvey P. Dale, Feb 23 2014 *)
PROG
(PARI) a(n)=for(i=1, 10+n^3, if(Mod(i-1, n)==0 && isprime((i-1)/n) && isprime(i*n+1), return(i)))
CROSSREFS
KEYWORD
nonn
AUTHOR
Amarnath Murthy, Mar 25 2004
EXTENSIONS
More terms from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 26 2004
STATUS
approved