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A185239
Numbers n such that (11^n + 10^n)/21 is prime.
4
53, 421, 647, 1601, 35527
OFFSET
1,1
COMMENTS
All terms are prime.
a(6) > 10^5.
MATHEMATICA
Select[ Prime[ Range[1, 100000] ], PrimeQ[ (11^# + 10^#)/21 ]& ]
PROG
(PARI) is(n)=ispseudoprime((11^n+10^n)/21) \\ Charles R Greathouse IV, May 22 2017
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Robert Price, Apr 05 2013
STATUS
approved