A377365 a(n) = least k such that 2n*5^k+1 is prime, or 0 if no prime is reached.

1, 2, 1, 1, 2, 1, 1, 2, 3, 1, 4, 2, 1, 2, 1, 3, 8, 1, 1, 1036, 1, 3, 2, 1, 1, 2, 1, 1, 2, 4, 1, 2, 1, 3, 6, 2, 257, 2, 2, 1, 40, 1, 1, 4, 2, 1, 2, 10, 1, 4, 2, 1, 6, 1, 3, 2, 1, 15, 4, 1, 79, 48, 1, 1, 2, 1, 5, 6, 1, 1, 6, 4, 3, 2, 1, 1, 2, 3, 3, 2, 1, 1, 6

Offset

1,2

Links

Table of n, a(n) for n=1..83.

Example

a(20) = 1036 because 40*5^k+1 is prime for k=1036 and not prime for k=1..1035.

Mathematica

f[n_, k_] := 2 n*5^k + 1;
s[n_] := Select[Range[5000], PrimeQ[f[n, #]] &, 1];
Flatten[Table[s[n], {n, 1, 500}]]

Crossrefs

Cf. A000040, A050412, A354747, A377364, A377366, A377367.

Sequence in context: A241911 A335221 A136610 * A326371 A226304 A101022

Adjacent sequences: A377362 A377363 A377364 * A377366 A377367 A377377

Keyword

nonn

Author

Clark Kimberling, Oct 31 2024

Status

approved