

A065083


The least k such that precisely n nearrepunit primes can be formed from (10^k1)/9 by changing one digit from 1 to 0.


5



1, 3, 8, 24, 20, 12, 488, 42, 162, 4848, 642, 1682
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OFFSET

0,2


COMMENTS



LINKS



EXAMPLE

a(5) = 12 because R_12 = (10^12 1)/9 = 111111111111 and from this number, by changing just one digit from 1 to 0, out of the eleven candidates, 111111111101, 111111110111, 111111011111, 111011111111 and 101111111111 are primes.


MATHEMATICA

a = Table[0, {10} ]; Do[p = IntegerDigits[ (10^n  1)/9]; c = 0; Do[ If[ q = FromDigits[ ReplacePart[p, 0, i]]; PrimeQ[q], c++ ], {i, 2, n} ]; If[ a[[c + 1]] == 0, a[[c + 1]] = n], {n, 1, 400} ]; a


PROG

(PARI) a(n)=my(k=1); while(sum(i=1, k2, ispseudoprime(10^k\910^i)) != n, k++); k \\ Charles R Greathouse IV, May 01 2012


CROSSREFS



KEYWORD

more,nonn,base


AUTHOR



EXTENSIONS

a(10)a(11) from comments and verified by Robert Price, Nov 04 2023


STATUS

approved



