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A181093
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p*(p+2)/3 where p and p+4 are primes.
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0
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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
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OFFSET
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1,1
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COMMENTS
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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).
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LINKS
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EXAMPLE
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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).
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MATHEMATICA
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# (# + 2)/3 & /@ Select[Prime@Range@140, PrimeQ[# + 4] &]
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PROG
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(PARI) {forprime (p=3, 10^3, isprime(p+4)&print1(p*(p+2)/3, ", "))}
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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