A080211 a(n) = binomial(n, smallest prime factor of n).

1, 1, 1, 6, 1, 15, 1, 28, 84, 45, 1, 66, 1, 91, 455, 120, 1, 153, 1, 190, 1330, 231, 1, 276, 53130, 325, 2925, 378, 1, 435, 1, 496, 5456, 561, 324632, 630, 1, 703, 9139, 780, 1, 861, 1, 946, 14190, 1035, 1, 1128, 85900584, 1225, 20825, 1326, 1, 1431, 3478761

Offset

1,4

Comments

For n>1: a(n)=1 iff n is prime.

Links

Robin Visser, Table of n, a(n) for n = 1..10000

Formula

a(n) = binomial(n, A020639(n)). - Michel Marcus, May 06 2020

Mathematica

Table[Binomial[n, FactorInteger[n][[1, 1]]], {n, 60}]  (* Harvey P. Dale, Apr 12 2011 *)

Prog

(PARI) a(n) = if (n==1, 1, binomial(n, vecmin(factor(n)[, 1]))); \\ Michel Marcus, May 06 2020
(Sage)
def a(n):
    if n==1: return 1
    return binomial(n, factor(n)[0][0])  # Robin Visser, Nov 25 2023

Crossrefs

Cf. A020639, A080212, A080213.

Sequence in context: A176121 A373845 A062190 * A146997 A147483 A050309

Adjacent sequences: A080208 A080209 A080210 * A080212 A080213 A080214

Keyword

nonn

Author

Reinhard Zumkeller, Feb 06 2003

Status

approved