

A069902


Largest prime factor of nth triangular number n(n+1)/2.


8



3, 3, 5, 5, 7, 7, 3, 5, 11, 11, 13, 13, 7, 5, 17, 17, 19, 19, 7, 11, 23, 23, 5, 13, 13, 7, 29, 29, 31, 31, 11, 17, 17, 7, 37, 37, 19, 13, 41, 41, 43, 43, 11, 23, 47, 47, 7, 7, 17, 17, 53, 53, 11, 11, 19, 29, 59, 59, 61, 61, 31, 7, 13, 13, 67
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OFFSET

2,1


COMMENTS

a(n) = A006530(A000217(n)).


LINKS

Table of n, a(n) for n=2..66.


EXAMPLE

A000217(9) = 9*(9+1)/2 = 45 = 3*3*5, therefore a(9) = 5.


MATHEMATICA

PrimeFactors[n_]:=Flatten[Table[ #[[1]], {1}]&/@FactorInteger[n]]; Table[PrimeFactors[n*(n1)/2][[ 1]], {n, 3, 6!}] (* Vladimir Joseph Stephan Orlovsky, Aug 12 2009 *)


PROG

(PARI) a(n)=vecmax(factor(n*(n+1)/2)[, 1]) \\ M. F. Hasler, May 02 2015


CROSSREFS

Cf. A069901, A069903, A069904. Essentially the same as A074399.
Sequence in context: A172170 A233808 A141424 * A085779 A078936 A293702
Adjacent sequences: A069899 A069900 A069901 * A069903 A069904 A069905


KEYWORD

nonn


AUTHOR

Reinhard Zumkeller, Apr 10 2002


STATUS

approved



