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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
OFFSET
0,6
COMMENTS
Conjecture: for all n, a(n)>0.
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
KEYWORD
nonn
AUTHOR
Vladimir Shevelev, Sep 14 2014
EXTENSIONS
More terms from Michel Marcus, Sep 16 2014
STATUS
approved