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A123704
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Numbers n such that (5^p-3^p)/2 is prime, where p = Prime[n].
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2
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6, 8, 9, 11, 15, 31, 48, 60, 314, 701, 940, 942
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Corresponding primes p = Prime[a(n)] are listed in A121877[n] = {13, 19, 23, 31, 47, 127, 223, 281, 2083, ...} Numbers n such that (5^n-3^n)/2 = [n] is a prime. Corresponding primes of the form (5^p - 3^p)/2 are listed in A123705[n] = {609554401, 9536162033329, 5960417405949649, 2328306127701998147089, 355271367866755685756083382145169, ...}.
Next term is greater than 1000. - Farideh Firoozbakht (mymontain(AT)yahoo.com), Oct 11 2006
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FORMULA
| a(n) = PrimePi[ A121877[n] ].
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MATHEMATICA
| Do[If[PrimeQ[(5^Prime[n] - 3^Prime[n])/2], Print[n]], {n, 1000}] (* Robert G. Wilson v (rgwv(AT)rgwv.com), Jan 12 2007 *)
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CROSSREFS
| Cf. A121877, A123705.
Sequence in context: A074845 A001746 A025070 * A045574 A074284 A125736
Adjacent sequences: A123701 A123702 A123703 * A123705 A123706 A123707
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KEYWORD
| nonn
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AUTHOR
| Alexander Adamchuk (alex(AT)kolmogorov.com), Oct 08 2006
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EXTENSIONS
| More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Oct 11 2006
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