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A103960
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Number of primes p such that prime(n)*p - 2 is prime and p <= prime(n).
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4
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1, 1, 2, 2, 2, 3, 1, 2, 4, 3, 2, 5, 3, 3, 5, 3, 4, 4, 4, 5, 6, 3, 4, 6, 3, 5, 6, 5, 3, 6, 5, 8, 5, 5, 6, 5, 7, 9, 7, 6, 6, 5, 7, 6, 8, 5, 8, 10, 5, 6, 8, 6, 7, 7, 10, 10, 3, 11, 8, 11, 6, 10, 8, 12, 9, 9, 7, 11, 9, 7, 8, 9, 6, 14, 8, 10, 11, 11, 12, 11, 7, 8
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OFFSET
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1,3
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COMMENTS
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Conjecture: All items of this sequence are greater than or equal to 1. Tested to prime(1000000).
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LINKS
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EXAMPLE
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Prime(1)*2-2 = 2, so a(1)=1;
Prime(3) = 5, 5*3-2 = 13, 5*5-2 = 23, so a(3)=2;
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MATHEMATICA
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Table[p=Prime[n]; ct=0; Do[pk=Prime[k]; If[PrimeQ[p*pk-2], ct=ct+1], {k, n}]; ct, {n, 100}]
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PROG
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(Haskell)
a103960 n = sum [a010051' $ p * q - 2 |
let p = a000040 n, q <- takeWhile (<= p) a000040_list]
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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STATUS
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approved
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