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A124522
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a(n) = smallest k such that 2nk-1 and 2nk+1 are primes.
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11
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2, 1, 1, 9, 3, 1, 3, 12, 1, 3, 9, 3, 12, 15, 1, 6, 3, 2, 6, 6, 1, 15, 3, 4, 3, 6, 2, 48, 6, 1, 21, 3, 3, 15, 6, 1, 27, 3, 4, 3, 15, 5, 12, 15, 2, 9, 3, 2, 9, 6, 1, 3, 60, 1, 6, 24, 2, 3, 9, 2, 129, 12, 7, 9, 15, 5, 12, 27, 1, 3, 9, 3, 42, 45, 1, 90, 3, 2, 66, 21, 5, 63, 27, 16, 6, 6, 2, 12, 24, 1, 6
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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MAPLE
| isA001359 := proc(n) RETURN( isprime(n) and isprime(n+2)) ; end: A124522 := proc(n) local k; k :=1 ; while true do if isA001359(2*n*k-1) then RETURN(k) ; fi ; k := k+1 ; od ; end: for n from 1 to 60 do printf("%d, ", A124522(n)) ; od ; - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 06 2006
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MATHEMATICA
| f[n_] := Block[{k = 1}, While[Nand @@ PrimeQ[{-1, 1} + 2n*k], k++ ]; k]; Table[f[n], {n, 91}] (*Chandler*)
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PROG
| (PARI) {for(n=1, 91, k=1; while(!isprime(2*n*k-1)||!isprime(2*n*k+1), k++); print1(k, ", "))}
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CROSSREFS
| Cf. A040040, A045753, A002822, A124065, A124518-A124522, A063983.
Sequence in context: A185814 A174553 A167015 * A016540 A132620 A156883
Adjacent sequences: A124519 A124520 A124521 * A124523 A124524 A124525
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KEYWORD
| nonn
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AUTHOR
| Artur Jasinski (grafix(AT)csl.pl), Nov 04 2006
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EXTENSIONS
| Edited and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 06 2006
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