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A063679
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Numbers n such that (3^n-7)/2 is prime.
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2
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0, 1, 4, 12, 18, 26, 106, 164, 246, 956, 2554, 3350
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,3
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COMMENTS
| x = 3^n is a solution to sigma(x - 7) = sigma(x) - 7 when (3^n - 7)/2 is prime.
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EXAMPLE
| (3^4-7)/2 = 37 is prime, so 4 is in the sequence.
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MAPLE
| with(numtheory):i := 0:x := 1:while i < 1000 do i := i+1:x := 3*x: if isprime((x-7)/2) then print(i):fi:od:
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MATHEMATICA
| Do[ If[ PrimeQ[ (3^n - 7)/2 ], Print[n] ], {n, 2, 5500} ]
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CROSSREFS
| Cf. A000203, A063680, A015913-A015917, A054905.
Sequence in context: A078514 A074285 A057311 * A075867 A071929 A008037
Adjacent sequences: A063676 A063677 A063678 * A063680 A063681 A063682
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KEYWORD
| nonn
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AUTHOR
| Jud McCranie (JudMcCranie(AT)ugaalum.uga.edu), Jul 28 2001
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EXTENSIONS
| More terms from Robert G. Wilson v (rgwv(AT)rgwv.com), Aug 02 2001
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