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A121877
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Numbers n such that (5^n - 3^n)/2 = A005059(n) is prime.
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45
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13, 19, 23, 31, 47, 127, 223, 281, 2083, 5281, 7411, 7433, 19051, 27239, 35863, 70327
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| All members are primes. Indices of primes in a(n), pi(a(n)), are listed in A123704 = {6, 8, 9, 11, 15, 31, 48, 60, 314, ...}. Corresponding primes of the form (5^p - 3^p)/2, where prime p = a(n), are listed in A123705 = {609554401, 9536162033329, 5960417405949649, 2328306127701998147089, 355271367866755685756083382145169, ...}.
No other terms < 125000. - Robert Price, Aug 15 2011
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FORMULA
| a(n) = prime(A123704(n)).
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MATHEMATICA
| Do[f=(5^n-3^n)/2; If[PrimeQ[f], Print[{n, f}]], {n, 1, 300}]
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PROG
| (PARI) forprime(p=2, 1e4, if(ispseudoprime((5^p-3^p)>>1), print1(p", "))) \\ Charles R Greathouse IV, Jun 16 2011
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CROSSREFS
| Cf. A005058, A005059, A109347, A120612, A081186, A121824, A123704, A123705.
Sequence in context: A113017 A007627 A180525 * A109902 A058898 A123840
Adjacent sequences: A121874 A121875 A121876 * A121878 A121879 A121880
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KEYWORD
| nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Aug 31 2006, Oct 08 2006
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EXTENSIONS
| More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Oct 11 2006
More terms a(13)-a(16) from Robert Price, Aug 15 2011
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