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A181093
p*(p+2)/3 where p and p+4 are primes.
0
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).
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
KEYWORD
nonn
AUTHOR
Zak Seidov, Jan 23 2011
EXTENSIONS
More terms from Michel Marcus, Mar 04 2014
STATUS
approved