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 A265629 Numbers k > 0 such that 10^(k+4) - 23 is prime. 2
 7, 13, 19, 31, 157, 761, 3469, 6883, 27677 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Numbers k such that '9977' appended to k times the digit 9 is prime. Up to a(8) the terms themselves are primes. LINKS FORMULA a(n) mod 2 = 1. - Altug Alkan, Dec 14 2015 EXAMPLE 7 appears because 99999999977 ('9' concatenated 7 times and prepended to '9977') is prime. MAPLE A265629:=n->`if`(isprime((10^(n+4) - 23), n, NULL): seq(A265629(n), n=1..1000) MATHEMATICA Select[ Range[10^3], PrimeQ[10^(# + 4) - 23] &] PROG (MAGMA) [n: n in [1..200] | IsPrime((10^(n+4) - 23)]; (PARI) is(n)=isprime(10^(n+4) - 23) CROSSREFS Cf. A260903. Sequence in context: A240971 A023255 A122482 * A283191 A048375 A198035 Adjacent sequences:  A265626 A265627 A265628 * A265630 A265631 A265632 KEYWORD nonn,base,more AUTHOR Mikk Heidemaa, Dec 11 2015 STATUS approved

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Last modified January 22 09:39 EST 2022. Contains 350481 sequences. (Running on oeis4.)