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A174213
Natural numbers n such that the concatenation n//1331 is a prime number.
7
6, 8, 9, 23, 29, 30, 32, 39, 42, 45, 53, 57, 65, 80, 92, 95, 101, 102, 108, 113, 116, 128, 141, 144, 153, 161, 182, 183, 186, 200, 206, 216, 218, 219, 225, 239, 245, 249, 260, 266, 270, 273, 279, 281, 282, 296, 311, 314, 318, 321
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