A076565 Greatest prime divisor of 2n+1 (sum of two successive integers).

3, 5, 7, 3, 11, 13, 5, 17, 19, 7, 23, 5, 3, 29, 31, 11, 7, 37, 13, 41, 43, 5, 47, 7, 17, 53, 11, 19, 59, 61, 7, 13, 67, 23, 71, 73, 5, 11, 79, 3, 83, 17, 29, 89, 13, 31, 19, 97, 11, 101, 103, 7, 107, 109, 37, 113, 23, 13, 17, 11, 41, 5, 127, 43, 131, 19, 5, 137, 139, 47, 13

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..10000

Formula

a(n) = A006530(2n+1). - Robert Israel, Mar 17 2017

Maple

seq(max(numtheory:-factorset(2*n+1)), n=1..200); # Robert Israel, Mar 17 2017

Mathematica

Table[FactorInteger[2n + 1][[-1, 1]], {n, 1, 100}] (* Indranil Ghosh, Mar 20 2017 *)

Prog

(PARI) for(n=1, 100, print1(vecmax(factor(2*n + 1)[, 1]), ", ")) \\ Indranil Ghosh, Mar 20 2017
(Python)
from sympy.ntheory import primefactors
print([max(primefactors(2*n + 1)) for n in range(1, 101)]) # Indranil Ghosh, Mar 20 2017

Crossrefs

Cf. A006530.

Sequence in context: A090368 A120374 A088836 * A286517 A377865 A199423

Adjacent sequences: A076562 A076563 A076564 * A076566 A076567 A076568

Keyword

easy,nonn

Author

Zak Seidov, Oct 19 2002

Status

approved