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A247341 Let b_k=3...3 consist of k>=1 3's. Then a(n) is the smallest k such that the concatenation 2^n b_k is prime, or a(n)=0 if there is no such prime. 4
1, 1, 1, 1, 1, 4, 1, 1, 2, 3, 1, 1, 4, 4, 6, 30, 3, 1, 6, 1, 32, 3, 3, 2, 22, 1, 6, 1, 2, 14, 7, 1, 10, 1, 2, 6, 3, 4, 2, 5, 2, 6, 1, 1, 37, 53, 53, 13, 64, 1, 67, 1, 45, 29, 17, 12, 14, 1, 2, 5, 15, 36, 10, 7, 1, 1, 81, 4, 18, 5, 55, 8, 33, 19, 8, 6, 2, 11 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,6

COMMENTS

Conjecture: for all n, a(n)>0.

LINKS

Table of n, a(n) for n=0..77.

PROG

(PARI) a(n) = {k = 0; while (! isprime(eval(concat(Str(2^n), Str((10^k-1)/3)))), k++); k; } \\ Michel Marcus, Sep 16 2014

CROSSREFS

Cf. A000079, A232210, A242775.

Sequence in context: A073693 A100261 A016526 * A030747 A222171 A325529

Adjacent sequences:  A247338 A247339 A247340 * A247342 A247343 A247344

KEYWORD

nonn

AUTHOR

Vladimir Shevelev, Sep 14 2014

EXTENSIONS

More terms from Michel Marcus, Sep 16 2014

STATUS

approved

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Last modified October 22 05:29 EDT 2019. Contains 328315 sequences. (Running on oeis4.)