A260880 Smallest k such that 1000...0//k (concatenation of 10^n and k) is prime.

1, 1, 9, 7, 3, 3, 37, 7, 7, 19, 3, 37, 31, 37, 61, 13, 3, 3, 39, 139, 57, 9, 49, 7, 67, 331, 319, 211, 57, 33, 49, 61, 103, 69, 67, 43, 321, 37, 3, 169, 63, 57, 31, 121, 9, 33, 217, 69, 9, 327, 171, 157, 31, 21, 279, 3, 193, 19, 67, 7, 121, 399, 57, 49, 49, 49

Offset

0,3

Links

Felix Fröhlich, Table of n, a(n) for n = 0..1000

Example

The smallest prime whose decimal expansion starts with 10^6 = 1000000 is 100000037, so a(6) = 37.

Prog

(PARI) a(n) = my(k=1); while(!ispseudoprime(eval(Str(10^n, k))), k++); k

Crossrefs

Similar to but different from A033873.

Sequence in context: A363766 A251734 A033873 * A135449 A060388 A081821

Adjacent sequences: A260877 A260878 A260879 * A260881 A260882 A260883

Keyword

nonn,base

Author

Felix Fröhlich, Aug 02 2015

Status

approved