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Search: id:A121877
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| A121877 |
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Numbers n such that (5^n - 3^n)/2 = A005059[n] is a prime. |
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46
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| 13, 19, 23, 31, 47, 127, 223, 281, 2083, 5281, 7411, 7433
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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All a(n) are primes. Indices of primes in a(n) are listed in A123704[n] = PrimePi[ a(n) ] = {6, 8, 9, 11, 15, 31, 48, 60, 314, ...} Numbers n such that (5^p-3^p)/2 is prime, where p = Prime[n]. Corresponding primes of the form (5^p - 3^p)/2, where prime p = a(n), are listed in A123705[n] = {609554401, 9536162033329, 5960417405949649, 2328306127701998147089, 355271367866755685756083382145169, ...}.
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FORMULA
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a(n) = Prime[ A123704[n] ].
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MATHEMATICA
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Do[f=(5^n-3^n)/2; If[PrimeQ[f], Print[{n, f}]], {n, 1, 300}]
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CROSSREFS
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Cf. A005058, A005059, A109347, A120612, A081186, A121824.
Cf. A123704, A123705.
Sequence in context: A038888 A113017 A007627 this_sequence A109902 A058898 A123840
Adjacent sequences: A121874 A121875 A121876 this_sequence A121878 A121879 A121880
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KEYWORD
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nonn
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AUTHOR
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Alexander Adamchuk (alex(AT)kolmogorov.com), Aug 31 2006, Oct 08 2006
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EXTENSIONS
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More terms from Farideh Firoozbakht (mymontain(AT)yahoo.com), Oct 11 2006
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