A361520 a(n) is the greatest prime factor of a(n-2)^2 + a(n-1)^2 where a(1)=2 and a(2)=3.

2, 3, 13, 89, 809, 349, 409, 144541, 10446133981, 1361264878245241, 4398505263882824939701, 17847523009215848981, 512996953133650208042047593649109478833

Offset: 1

Author

Sebastian F. Orellana, Mar 14 2023

Keywords

• nonn

Links

• Sebastian F. Orellana, Table of n, a(n) for n = 1..15

Crossrefs

Cf. A006530, A113494, A175723.

Programs

Maple

A[1]:= 2: A[2]:= 3:
for n from 3 to 15 do A[n]:= max(numtheory:-factorset(A[n-2]^2 + A[n-1]^2)) od:
seq(A[],n=1..15); # Robert Israel, Mar 17 2023

Mathematica

a[1] = 2; a[2] = 3; a[n_] := a[n] = FactorInteger[a[n - 1]^2 + a[n - 2]^2][[-1, 1]]; Array[a, 14] (* Amiram Eldar, Mar 14 2023 *)