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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
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.
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: A023255 A373584 A122482 * A283191 A048375 A198035
KEYWORD
nonn,base,more
AUTHOR
Mikk Heidemaa, Dec 11 2015
STATUS
approved