A361520 - OEIS

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

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OFFSET

1,1

LINKS

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

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 *)

CROSSREFS

Cf. A006530, A113494, A175723.

Sequence in context: A212433 A013167 A224239 * A068096 A098462 A125283

Adjacent sequences: A361517 A361518 A361519 * A361521 A361522 A361523

KEYWORD

nonn

AUTHOR

Sebastian F. Orellana, Mar 14 2023

STATUS

approved