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A121938 Primes of the form (3^n + 5^n)/2^3 = A074606[n]/8. 2
19, 421, 10039, 95383574161, 2384331073699, 1925929944387235853055979210606894889560480247048440342330377620014353281101 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Corresponding numbers n such that (3^n + 5^n)/8 is prime are listed in A122853[n] = {3,5,7,17,19,109,509,661,709,1231,...}. All these numbers are primes. - Alexander Adamchuk, Sep 14 2006

The next term is too large to include. - Alexander Adamchuk, Sep 14 2006

LINKS

Table of n, a(n) for n=1..6.

FORMULA

a(n) = (A122853(n)^3 + A122853(n)^5)/8. a(n) = A074606[A122853(n)]/8 = A081186[A122853(n)]/4. a(n) = A079773[A122853(n)]. - Alexander Adamchuk, Sep 14 2006

MATHEMATICA

Do[f=5^n+3^n; If[PrimeQ[f/2^3], Print[{n, f/2^3}]], {n, 1, 1231}] - Alexander Adamchuk, Sep 14 2006

CROSSREFS

Cf. A074706, A122853, A081186, A079773, A121824, A121877, A005058, A005059, A121938, A109347.

Sequence in context: A077716 A089573 A284332 * A291644 A108145 A114350

Adjacent sequences:  A121935 A121936 A121937 * A121939 A121940 A121941

KEYWORD

nonn

AUTHOR

Zak Seidov, Sep 10 2006

EXTENSIONS

More terms from Alexander Adamchuk, Sep 14 2006

STATUS

approved

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Last modified August 8 05:50 EDT 2020. Contains 336290 sequences. (Running on oeis4.)