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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
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
KEYWORD
nonn
AUTHOR
Reinhard Zumkeller, Mar 11 2003
STATUS
approved

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Last modified June 19 23:45 EDT 2024. Contains 373510 sequences. (Running on oeis4.)