A075753 Smallest prime factor of n-th odd triangular number.

3, 3, 3, 3, 5, 7, 3, 3, 3, 3, 11, 5, 3, 3, 3, 3, 5, 19, 3, 3, 3, 3, 23, 5, 3, 3, 3, 3, 29, 31, 3, 3, 3, 3, 5, 37, 3, 3, 3, 3, 41, 5, 3, 3, 3, 3, 5, 7, 3, 3, 3, 3, 53, 5, 3, 3, 3, 3, 7, 11, 3, 3, 3, 3, 5, 7, 3, 3, 3, 3, 11, 5, 3, 3, 3, 3, 5, 79, 3, 3, 3, 3, 83, 5, 3, 3, 3, 3, 89, 7, 3, 3, 3, 3, 5, 97, 3, 3, 3

Offset

1,1

Comments

As A014493(n)=binomial(A042963(n),2) and a(n)=A020639(A014493(n))>2, A014493(n) is a good binomial coefficient.

Links

Table of n, a(n) for n=1..99.

Eric Weisstein's World of Mathematics, Triangular Number.

Eric Weisstein's World of Mathematics, Good Binomial Coefficient.

Eric Weisstein's World of Mathematics, Least Prime Factor.

Mathematica

FactorInteger[#][[1, 1]]&/@Rest[Select[Accumulate[Range[200]], OddQ]] (* Harvey P. Dale, Jul 30 2016 *)

Crossrefs

Cf. A069901.

Sequence in context: A339971 A156724 A196186 * A006166 A339718 A349926

Adjacent sequences: A075750 A075751 A075752 * A075754 A075755 A075756

Keyword

nonn

Author

Reinhard Zumkeller, Mar 11 2003

Status

approved