OFFSET
1,1
COMMENTS
n is no multiple of 11 as 1331 = 11^3.
Necessarily n = 3 * k or n = 3 * k + 2, but not n = 3 * k + 1, because sod(1331) = 8.
Sequence is infinite, Dirichlet's prime number theorem for naturals of the form n * 10^4 + 1331.
For prefixed 1331 and references see A173836.
EXAMPLE
61331 = prime(6169) => a(1) = 6.
81331 = prime(7958) => a(2) = 8.
MATHEMATICA
Select[Range[400], PrimeQ[#*10^4+1331]&] (* Harvey P. Dale, Jan 17 2019 *)
PROG
(PARI) isok(n) = isprime(n*10^4 + 1331); \\ Michel Marcus, Aug 27 2013
CROSSREFS
KEYWORD
base,nonn
AUTHOR
Eva-Maria Zschorn (e-m.zschorn(AT)zaschendorf.km3.de), Mar 12 2010
STATUS
approved