A079083 Smallest odd prime factor of (prime(n)+1)*(prime(n+1)+1)/4.

3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 19, 3, 3, 3, 3, 3, 3, 17, 3, 3, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 19, 41, 3, 3, 3, 3, 3, 3, 3, 3, 5, 7, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 17, 3, 3, 3, 3, 3, 3, 3, 3, 13, 3, 3, 3, 3, 3, 11, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 5, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 3, 131, 137

Offset: 1

Author

Reinhard Zumkeller, Dec 22 2002

Keywords

• nonn

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A078701, A079079, A079084.

Programs

Haskell

a079083 = a078701 . a079079  -- Reinhard Zumkeller, Oct 08 2012

Mathematica

odd[n_] := n / 2^IntegerExponent[n, 2]; a[n_] := FactorInteger[odd[(Prime[n]+1)*(Prime[n+1]+1)]][[1, 1]]; Array[a, 100] (* Amiram Eldar, Apr 06 2025 *)

PARI

odd(n) = n >> valuation(n, 2);
a(n) = factor(odd((prime(n)+1)*(prime(n+1)+1)))[1, 1]; \\ Amiram Eldar, Apr 06 2025

Formula

a(n) = A078701(A079079(n)).