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 A092961 Least k such that (k-1)/n and k*n + 1 both are primes. 3
 4, 5, 10, 9, 26, 13, 78, 17, 64, 21, 56, 61, 40, 239, 46, 81, 290, 55, 58, 41, 148, 45, 162, 73, 76, 131, 136, 57, 320, 61, 528, 65, 100, 69, 666, 253, 186, 77, 118, 681, 206, 85, 130, 89, 136, 231, 236, 97, 148, 101, 562, 885, 372, 163, 606, 113, 628, 175, 650, 181 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Obviously a(n) is odd or even as n is even or odd. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE a(4) = 9 as (9-1)/4 = 2 and 9*4 + 1 = 37 both are primes. a(9) = 64, (64-1)/9 = 7 and 64*9 + 1 = 577 both are primes. MATHEMATICA bp[n_]:=Module[{k=2n+1}, While[!PrimeQ[(k-1)/n]||!PrimeQ[k*n+1], k++]; k]; Array[bp, 60] (* Harvey P. Dale, Feb 23 2014 *) PROG (PARI) a(n)=for(i=1, 10+n^3, if(Mod(i-1, n)==0 && isprime((i-1)/n) && isprime(i*n+1), return(i))) CROSSREFS Cf. A092962, A092963. Sequence in context: A060648 A263828 A327577 * A327614 A177711 A115945 Adjacent sequences:  A092958 A092959 A092960 * A092962 A092963 A092964 KEYWORD nonn AUTHOR Amarnath Murthy, Mar 25 2004 EXTENSIONS More terms from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 26 2004 STATUS approved

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Last modified September 17 14:07 EDT 2021. Contains 347478 sequences. (Running on oeis4.)