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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
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).
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: A322634 A378842 A108535 * A237527 A015019 A225165
KEYWORD
nonn,base,hard,more
AUTHOR
Mikk Heidemaa, Dec 02 2015
STATUS
approved