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

1,1

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).

Links

Table of n, a(n) for n=1..39.

Example

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).

Mathematica

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

Prog

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

Crossrefs

Cf. A014641.

Sequence in context: A342379 A146822 A146223 * A055384 A271540 A272987

Adjacent sequences: A181090 A181091 A181092 * A181094 A181095 A181096

Keyword

nonn

Author

Zak Seidov, Jan 23 2011

Extensions

More terms from Michel Marcus, Mar 04 2014

Status

approved