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A260880 Smallest k such that 1000...0//k (concatenation of 10^n and k) is prime. 1
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 (list; graph; refs; listen; history; text; internal format)
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: A002205 A251734 A033873 * A135449 A060388 A081821

Adjacent sequences:  A260877 A260878 A260879 * A260881 A260882 A260883

KEYWORD

nonn,base

AUTHOR

Felix Fröhlich, Aug 02 2015

STATUS

approved

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Last modified October 6 20:00 EDT 2022. Contains 357270 sequences. (Running on oeis4.)