A123704 - OEIS

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A123704

Numbers k such that (5^p - 3^p)/2 is prime, where p = prime(k).

2

6, 8, 9, 11, 15, 31, 48, 60, 314, 701, 940, 942, 2164, 2981, 3810, 6971, 12068, 13641, 16502, 68800

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OFFSET

1,1

COMMENTS

The corresponding primes p = prime(a(n)) are listed in A121877.

The corresponding primes of the form (5^p - 3^p)/2 are listed in A123705.

a(13) is greater than 1000. - Farideh Firoozbakht, Oct 11 2006

LINKS

Table of n, a(n) for n=1..20.

FORMULA

a(n) = primepi(A121877(n)).

MATHEMATICA

Do[If[PrimeQ[(5^Prime[n] - 3^Prime[n])/2], Print[n]], {n, 1000}] (* Robert G. Wilson v, Jan 12 2007 *)

PrimePi[#]&/@Select[Prime[Range[1000]], PrimeQ[(5^#-3^#)/2]&] (* Harvey P. Dale, Sep 23 2018 *)

CROSSREFS

Cf. A005059, A121877, A123705.

Sequence in context: A074845 A001746 A025070 * A045574 A074284 A125736

Adjacent sequences: A123701 A123702 A123703 * A123705 A123706 A123707

KEYWORD

nonn,more

AUTHOR

Alexander Adamchuk, Oct 08 2006

EXTENSIONS

More terms from Farideh Firoozbakht, Oct 11 2006

a(13)-a(16) computed from A121877 by Jinyuan Wang, Mar 23 2020

a(17)-a(19) from Kellen Shenton, May 18 2022

a(20) from Amiram Eldar, Sep 06 2024

STATUS

approved