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 A281407 Numbers k such that (292*10^k - 1)/3 is prime. 0
 0, 2, 4, 9, 14, 20, 28, 33, 156, 285, 302, 1121, 1300, 2540, 3873, 4706, 5297, 7292, 11086, 15928, 16203, 17267, 17793, 19326, 32009, 67659 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers such that the digits 97 followed by k occurrences of the digit 3 is prime (see Example section). a(27) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 973w3. EXAMPLE 2 is in this sequence because (292*10^2 - 1)/3 = 9733 is prime. Initial terms and primes associated: a(1) = 0, 97; a(2) = 2, 9733; a(3) = 4, 973333; a(4) = 9, 97333333333; a(5) = 14, 9733333333333333; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[(292*10^# - 1)/3] &] PROG (PARI) isok(n) = isprime((292*10^n - 1)/3); \\ Michel Marcus, Jan 21 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A234899 A190553 A270532 * A078671 A119637 A169762 Adjacent sequences:  A281404 A281405 A281406 * A281408 A281409 A281410 KEYWORD nonn,more,hard AUTHOR Robert Price, Jan 21 2017 STATUS approved

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Last modified May 26 13:59 EDT 2022. Contains 354092 sequences. (Running on oeis4.)