The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A065083 The least k such that precisely n near-repunit primes can be formed from (10^k-1)/9 by changing one digit from 1 to 0. 5
 1, 3, 8, 24, 20, 12, 488, 42, 162, 4848, 642, 1682 (list; graph; refs; listen; history; text; internal format)
 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 a(>11) > 5000. - Robert Price, Nov 06 2023 LINKS Table of n, a(n) for n=0..11. Chris Caldwell, Below are all of the 12-digit Near-Repunit 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, k-2, ispseudoprime(10^k\9-10^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 a(9) from Robert Price, Nov 04 2023 a(10)-a(11) from comments and verified by Robert Price, Nov 04 2023 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 8 03:15 EST 2023. Contains 367662 sequences. (Running on oeis4.)