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
Examples
The smallest prime whose decimal expansion starts with 10^6 = 1000000 is 100000037, so a(6) = 37.
Links
- Felix Fröhlich, Table of n, a(n) for n = 0..1000
Crossrefs
Similar to but different from A033873.
Programs
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PARI
a(n) = my(k=1); while(!ispseudoprime(eval(Str(10^n, k))), k++); k