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A128024
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Numbers k such that (7^k - 3^k)/4 is prime.
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29
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3, 7, 19, 109, 131, 607, 863, 2917, 5923, 12421, 187507, 353501, 817519
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OFFSET
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1,1
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COMMENTS
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All terms are primes. No other terms < 1000000.
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LINKS
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MATHEMATICA
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k=4; Select[ Prime[ Range[1, 200] ], PrimeQ[ ((k+3)^# - 3^#)/k ]& ]
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PROG
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(Python)
from sympy import isprime
def aupto(lim): return [k for k in range(lim+1) if isprime((7**k-3**k)//4)]
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CROSSREFS
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KEYWORD
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hard,more,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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