A377364 a(n) = least k such that 2n*3^k-2 is prime, or 0 if no prime is reached.
1, 1, 1, 2, 1, 1, 1, 3, 2, 1, 1, 1, 1, 3, 2, 1, 1, 1, 4, 5, 1, 2, 1, 2, 1, 1, 1, 9, 2, 1, 4, 1, 1, 2, 1, 5, 1, 1, 11, 1, 2, 2, 4, 3, 1, 1, 1, 3, 2, 4, 1, 1, 5, 3, 1, 1, 3, 1, 2, 4, 1, 1, 1, 2, 2, 1, 5, 1, 3, 1, 2, 1, 1, 8, 3, 1, 1, 4, 2, 80, 1, 6, 1, 8, 2, 2
Offset: 1
Keywords
Examples
a(20) = 5 because 40*3^5 + 1 is prime and 40*3^k + 1 is not prime for k=1..4.
Programs
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Mathematica
{b, h} = {3, 2}; f[n_, k_] := n*b^k - h s[n_] := Select[Range[20], PrimeQ[f[n, #]] &, 1] Flatten[Table[s[n], {n, 1, 200}]]