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 A291605 Numbers k such that 5*10^k + 41 is prime. 0
 2, 5, 8, 24, 35, 116, 208, 231, 237, 303, 1451, 1512, 2235, 2612, 4433, 4499, 5408, 7331, 11896, 12821, 23679, 23900, 59650, 122082, 151257, 159656 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS For k>1, numbers such that the digit 5 followed by k-2 occurrences of the digit 0 followed by the digits 41 is prime (see Example section). a(27) > 2*10^5. LINKS Makoto Kamada, Factorization of near-repdigit-related numbers. Makoto Kamada, Search for 50w41 EXAMPLE 2 is in this sequence because 5*10^2 + 41 = 541 is prime. Initial terms and primes associated: a(1) = 2, 541; a(2) = 5, 500041; a(3) = 8, 500000041; a(4) = 24, 5000000000000000000000041; a(5) = 35, 500000000000000000000000000000000041; etc. MATHEMATICA Select[Range[0, 100000], PrimeQ[5*10^# + 41] &] PROG (PARI) isok(k) = ispseudoprime(5*10^k + 41); \\ Altug Alkan, Aug 27 2017 CROSSREFS Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. Sequence in context: A195295 A088144 A100501 * A142869 A086825 A192476 Adjacent sequences:  A291602 A291603 A291604 * A291606 A291607 A291608 KEYWORD nonn,more,hard AUTHOR Robert Price, Aug 27 2017 EXTENSIONS a(24)-a(26) from Robert Price, Mar 07 2019 STATUS approved

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Last modified August 7 08:55 EDT 2020. Contains 336274 sequences. (Running on oeis4.)