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.
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
KEYWORD
nonn,base,more
AUTHOR
Mikk Heidemaa, Dec 11 2015
STATUS
approved