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A224748
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Given n-th prime p, a(n) = number of primes of the form p + q - 1 where q is any prime < p.
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14
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0, 0, 1, 1, 2, 3, 3, 3, 2, 3, 6, 6, 5, 8, 4, 4, 4, 11, 11, 8, 9, 11, 4, 5, 13, 9, 11, 7, 13, 5, 17, 10, 9, 15, 7, 19, 17, 18, 10, 8, 8, 25, 12, 17, 12, 18, 29, 23, 12, 21, 12, 15, 28, 18, 11, 11, 12, 32, 25, 19, 22, 14, 29, 17, 27, 14, 40, 36, 18, 29, 16, 13
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OFFSET
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1,5
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COMMENTS
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LINKS
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MAPLE
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a:= n-> add(`if`(isprime(ithprime(n)+ithprime(i)-1), 1, 0), i=1..n-1):
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MATHEMATICA
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Table[p = Prime[n]; c = 0; i = 1; While[i < n, If[PrimeQ[p + Prime[i] - 1], c = c + 1]; i++]; c, {n, 72}]
Table[Count[Prime[n]+Prime[Range[n-1]]-1, _?PrimeQ], {n, 80}] (* Harvey P. Dale, Nov 04 2020 *)
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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