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A092961
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Least k so that (k-1)/n and k*n + 1 both are primes.
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2
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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; internal format)
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OFFSET
| 1,1
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COMMENTS
| Obviously a(n) is odd or even as n is even or odd.
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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.
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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)))
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CROSSREFS
| Cf. A092962, A092963.
Sequence in context: A042427 A009778 A060648 * A177711 A115945 A084750
Adjacent sequences: A092958 A092959 A092960 * A092962 A092963 A092964
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KEYWORD
| nonn
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AUTHOR
| Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Mar 25 2004
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EXTENSIONS
| More terms from Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 26 2004
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