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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 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 August 12 05:33 EDT 2020. Contains 336438 sequences. (Running on oeis4.)