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A016014 Least k such that 2*n*k + 1 is a prime. 12
1, 1, 1, 2, 1, 1, 2, 1, 1, 2, 1, 3, 2, 1, 1, 3, 3, 1, 5, 1, 1, 2, 1, 2, 2, 1, 2, 2, 1, 1, 5, 3, 1, 2, 1, 1, 2, 3, 1, 3, 1, 4, 2, 1, 2, 3, 3, 1, 2, 1, 1, 3, 1, 1, 3, 1, 2, 2, 6, 2, 3, 3, 1, 2, 1, 3, 2, 1, 1, 2, 4, 3, 2, 1, 1, 3, 3, 1, 2, 4, 1, 5, 1, 2, 6, 1, 2, 2, 1, 1, 3, 7, 2, 5, 1, 1, 2, 1, 1 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,4

COMMENTS

Records are 1, 2, 3, 5, 6, 7, 10, 12, 15, 17,...(A239746) at n = 1, 4, 12, 19, 59, 92, 159, 227, 256, 514,...(A239727)  - Zak Seidov, Mar 25 2014

Is the sequence bounded? - Zak Seidov, Mar 25 2014

Answer: No, for any given N a number n such that a(n) > N can be constructed by the Chinese Remainder Theorem, see A239727. - Charles R Greathouse IV, Mar 25 2014

a(n) = 1 for n in A005097. - Robert Israel, Oct 26 2016

LINKS

Zak Seidov, Table of n, a(n) for n = 1..10000

MAPLE

f:= proc(n) local k;

     for k from 1 do if isprime(2*n*k+1) then return k fi od

end proc:

map(f, [$1..100]); # Robert Israel, Oct 26 2016

MATHEMATICA

Do[k = 1; cp = n*k + 1; While[ ! PrimeQ[cp], k++; cp = n*k + 1]; Print[k], {n, 2, 400, 2}] (* Lei Zhou, Feb 23 2005 *)

PROG

(PARI) a(n)=my(k); while(!isprime(2*n*(k++)+1), ); k \\ Charles R Greathouse IV, Mar 25 2014

CROSSREFS

Cf. A005097, A103961, A239746, A239727.

A070846 contains the corresponding primes.

Sequence in context: A076845 A161906 A204901 * A067760 A078680 A296072

Adjacent sequences:  A016011 A016012 A016013 * A016015 A016016 A016017

KEYWORD

nonn

AUTHOR

Robert G. Wilson v

STATUS

approved

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Last modified January 20 14:40 EST 2019. Contains 319333 sequences. (Running on oeis4.)