A080215 - OEIS

A080215

Binomial(greatest prime factor of n, smallest odd prime factor of n).

1, 2, 1, 2, 1, 1, 1, 2, 1, 1, 1, 1, 1, 1, 10, 2, 1, 1, 1, 1, 35, 1, 1, 1, 1, 1, 1, 1, 1, 10, 1, 2, 165, 1, 21, 1, 1, 1, 286, 1, 1, 35, 1, 1, 10, 1, 1, 1, 1, 1, 680, 1, 1, 1, 462, 1, 969, 1, 1, 10, 1, 1, 35, 2, 1287, 165, 1, 1, 1771, 21, 1, 1, 1, 1, 10, 1, 330, 286, 1, 1, 1, 1, 1, 35

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OFFSET

1,2

LINKS

Antti Karttunen, Table of n, a(n) for n = 1..16384

FORMULA

a(n) = binomial(A006530(n), A078701(n)). - Antti Karttunen, Dec 23 2018

MATHEMATICA

a[n_] := With[{f = Select[FactorInteger[n], #[[1]] != 2&]}, If[f == {}, 2, Binomial[f[[-1, 1]], f[[1, 1]]]]];

Array[a, 100] (* Jean-François Alcover, Dec 02 2021 *)

PROG

(PARI) A080215(n) = if(1==n, n, my(f = factor(n)[, 1], v = select(x->((x%2)==1), f)); binomial(f[#f], if(#v, vecmin(v), 1))); \\ Antti Karttunen, Dec 23 2018

CROSSREFS

Cf. A006530, A078701, A080214, A080212.

Sequence in context: A286299 A081729 A219157 * A266871 A331290 A060500

Adjacent sequences: A080212 A080213 A080214 * A080216 A080217 A080218

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Feb 06 2003

STATUS

approved