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A296029 Numbers k such that 10^k/8 - 1 is prime. 1
4, 7, 8, 11, 16, 22, 28, 29, 79, 91, 170, 293, 392, 1898, 2597, 3641, 4099, 8236, 11393, 17969, 18503 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Searched up to k=20000. - Michael B. Porter, Dec 07 2017

Equivalently, numbers k such that 125*10^(k-3) - 1 is prime.

LINKS

Table of n, a(n) for n=1..21.

EXAMPLE

1249, 1249999, and 12499999 are prime, so 4, 7, and 8 are in the sequence.

MATHEMATICA

Select[Range[2000], PrimeQ[10^#/8 - 1] &] (* Michael De Vlieger, Dec 08 2017 *)

PROG

(PARI) lista(nn) = for(n=4, nn, if(ispseudoprime(10^n/8 - 1), print1(n, ", "))) \\ Iain Fox, Dec 04 2017

CROSSREFS

Sequence in context: A137362 A190765 A024621 * A000606 A215458 A061932

Adjacent sequences:  A296026 A296027 A296028 * A296030 A296031 A296032

KEYWORD

nonn,more

AUTHOR

Patrick A. Thomas, Dec 03 2017

EXTENSIONS

a(12), a(13), a(15), a(16) from Jon E. Schoenfield, Dec 03 2017

a(14) and a(17)-a(21) from Michael B. Porter, Dec 07 2017

STATUS

approved

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Last modified November 22 13:47 EST 2019. Contains 329393 sequences. (Running on oeis4.)