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 A265123 Numbers n such that (2^(n+3) * 5^(n+4) - 1463)/9 is prime (n > 0). 1
 1, 5, 155, 353, 1144, 4297, 11921, 14027 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Numbers n such that '393' appended to n times the digit 5 is prime. Up to a(7) nonprimes alternate with primes; a(9) > 30000 (if it exists). LINKS EXAMPLE 1 appears because 5393 is prime. 5 appears because 55555393 ('5' concatenated 5 times and prepended to '393') is prime. MAPLE A265123:=n->`if`(isprime((2^(n+3) * 5^(n+4) - 1463)/9), n, NULL): seq(A265123(n), n=1..1500); MATHEMATICA Select[Range[1500], PrimeQ[(2^(# + 3) * 5^(# + 4) - 1463) / 9] &] PROG (MAGMA) [n: n in [1..400] | IsPrime((2^(n+3) * 5^(n+4) - 1463) div 9)]; (PARI) is(n)=isprime((2^(n+3)*5^(n+4) - 1463)/9) CROSSREFS Cf. A260903. Sequence in context: A208578 A322634 A108535 * A237527 A015019 A225165 Adjacent sequences:  A265120 A265121 A265122 * A265124 A265125 A265126 KEYWORD nonn,base,hard,more AUTHOR Mikk Heidemaa, Dec 02 2015 STATUS approved

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Last modified October 15 00:14 EDT 2019. Contains 328025 sequences. (Running on oeis4.)