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A053989 Smallest k such that nk-1 is prime. 15
3, 2, 1, 1, 4, 1, 2, 1, 2, 2, 4, 1, 8, 1, 2, 2, 4, 1, 2, 1, 2, 2, 6, 1, 6, 4, 2, 3, 6, 1, 2, 1, 4, 2, 4, 2, 2, 1, 6, 2, 4, 1, 6, 1, 2, 3, 6, 1, 2, 3, 2, 2, 4, 1, 2, 3, 2, 3, 6, 1, 8, 1, 4, 2, 6, 2, 6, 1, 2, 2, 4, 1, 14, 1, 2, 2, 4, 3, 2, 1, 8, 2, 4, 1, 6, 3, 2, 3, 16, 1, 2, 4, 6, 3, 4, 2, 2, 1, 2, 2 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

a(n) = (A038700(n)+1)/n.

EXAMPLE

a(5)=4 because the smallest prime in the sequence 5k-1 (4,9,14,19,24...) is 19 when k=4

PROG

(Haskell)

a053989 n = head [k | k <- [1..], a010051' (k * n - 1) == 1]

-- Reinhard Zumkeller, Feb 14 2013

(PARI) a(n)=my(j); while(!isprime(j++*n-1), ); j \\ Charles R Greathouse IV, Apr 18 2013

CROSSREFS

Cf. A034693, A038700, A071558, A010051, A103689, A200996.

Sequence in context: A188316 A197027 A143772 * A239938 A097794 A275494

Adjacent sequences:  A053986 A053987 A053988 * A053990 A053991 A053992

KEYWORD

easy,nonn

AUTHOR

Henry Bottomley, Apr 04 2000

STATUS

approved

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Last modified October 29 19:29 EDT 2020. Contains 338069 sequences. (Running on oeis4.)