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A075753 Smallest prime factor of n-th odd triangular number. 0
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 (list; graph; refs; listen; history; text; internal format)
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: A129756 A156724 A196186 * A006166 A268443 A142716

Adjacent sequences:  A075750 A075751 A075752 * A075754 A075755 A075756

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, Mar 11 2003

STATUS

approved

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Last modified February 18 09:39 EST 2020. Contains 332011 sequences. (Running on oeis4.)