A181093 p*(p+2)/3 where p and p+4 are primes.

5, 21, 65, 133, 481, 645, 1541, 2133, 3201, 3605, 4033, 5461, 8965, 12545, 16725, 17633, 25761, 31621, 32865, 40833, 48133, 52801, 64533, 69921, 71765, 79381, 83333, 125665, 138245, 151425, 182533, 191521, 197633, 226325, 243105, 246533, 256961, 260485, 274821

Offset: 1

Author

Zak Seidov, Jan 23 2011

Keywords

• nonn

Comments

For p>3, p == 1 mod 6 and p(p+2) == 0 mod 3, hence, except for the first term, a(n) = subsequence of A014641 Odd octagonal numbers: (2n+1)(6n+1).

Examples

			p=3,p+4=7 are primes and a(1)=3*5/3=3,
p=7,p+4=11 are primes and a(2)=7*9/3=21=A014641(2),
p=13,p+4=17 are primes and a(3)=13*15/3=65=A014641(3).
		

Crossrefs

Cf. A014641.

Programs

Mathematica

# (# + 2)/3 & /@ Select[Prime@Range@140, PrimeQ[# + 4] &]

PARI

{forprime (p=3,10^3,isprime(p+4)&print1(p*(p+2)/3,","))}

Extensions

More terms from Michel Marcus, Mar 04 2014