

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.


4




OFFSET

0,2


COMMENTS

Least inverse of A034093.  Charles R Greathouse IV, May 01 2012
a(10) = 642 and a(11) = 1682.  Charles R Greathouse IV, May 03 2012


LINKS

Table of n, a(n) for n=0..8.
Chris Caldwell, Below are all of the 12digit NearRepunit primes:
Chris Caldwell, Repunits


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

Cf. A034093, A002275, A065074.
Sequence in context: A327151 A317362 A309114 * A280190 A037450 A081990
Adjacent sequences: A065080 A065081 A065082 * A065084 A065085 A065086


KEYWORD

more,nonn,base


AUTHOR

Robert G. Wilson v, Nov 19 2001


EXTENSIONS

a(6) from Charles R Greathouse IV, May 01 2012


STATUS

approved



