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A253772
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Numbers k such that 4^k + 13 is prime.
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8
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1, 2, 4, 10, 19, 32, 40, 146, 566, 2054, 9967, 62639, 87814, 141092
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OFFSET
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1,2
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COMMENTS
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Numbers of the form 4^n+k (for n>0) are never primes when k is even (obviously) or when k == -1 (mod 6): in the last case, in fact, (3+1)^n + 6*h-1 is divisible by 3. - Bruno Berselli, Oct 06 2015
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LINKS
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FORMULA
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MATHEMATICA
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Select[Range[4000], PrimeQ[4^# + 13] &]
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PROG
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(Magma) [n: n in [0..2000] | IsPrime(4^n+13)];
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CROSSREFS
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Cf. Numbers k such that 4^k + d is prime: A089437 (d=3), A217349 (d=7), A217350 (d=9), this sequence (d=13), A253773 (d=15), A253774 (d=19), A262345 (d=21), A204388 (d=25), A262969 (d=27), A262971 (d=31), A262972 (d=33).
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KEYWORD
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nonn,more
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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