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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
OFFSET
1,1
COMMENTS
Corresponding numbers n such that (3^n + 5^n)/8 is prime are listed in A122853. All these numbers are primes. - Alexander Adamchuk, Sep 14 2006
The next term is too large to include. - Alexander Adamchuk, Sep 14 2006
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 *)
KEYWORD
nonn
AUTHOR
Zak Seidov, Sep 10 2006
EXTENSIONS
More terms from Alexander Adamchuk, Sep 14 2006
STATUS
approved