%N Index of the largest prime which divides n(n+1).
%C Yields the row of A145605 in which n appears, and also the first row of A138180 in which n appears.
%F a(n) = pi(A074399(n)), where pi = A000720.
%o (PARI) a(n)=primepi(vecmax(factor(n*(n+1))[,1]))
%Y Cf. A002071, A145604, A138180, A145605, A002072, A074399.
%A _M. F. Hasler_, Jan 16 2015