

A252489


Index of the largest prime which divides n(n+1).


3



1, 2, 2, 3, 3, 4, 4, 2, 3, 5, 5, 6, 6, 4, 3, 7, 7, 8, 8, 4, 5, 9, 9, 3, 6, 6, 4, 10, 10, 11, 11, 5, 7, 7, 4, 12, 12, 8, 6, 13, 13, 14, 14, 5, 9, 15, 15, 4, 4, 7, 7, 16, 16, 5, 5, 8, 10, 17, 17, 18, 18, 11, 4, 6, 6, 19, 19, 9, 9, 20, 20, 21, 21, 12, 8, 8, 6
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OFFSET

1,2


COMMENTS

Yields the row of A145605 in which n appears, and also the first row of A138180 in which n appears.


LINKS

Robert Israel, Table of n, a(n) for n = 1..10000


FORMULA

a(n) = pi(A074399(n)), where pi = A000720.
a(n) = max(A061395(n),A061395(n+1)).  Robert Israel, Feb 12 2021


MAPLE

A061395:= [1, seq(numtheory:pi(max(numtheory:factorset(n))), n=2..101)]:
zip(max, A061395[1..2], A061395[2..1]); # Robert Israel, Feb 12 2021


PROG

(PARI) a(n)=primepi(vecmax(factor(n*(n+1))[, 1]))


CROSSREFS

Cf. A002071, A145604, A138180, A145605, A002072, A074399, A061395.
Sequence in context: A106747 A335979 A083447 * A332250 A340321 A340320
Adjacent sequences: A252486 A252487 A252488 * A252490 A252491 A252492


KEYWORD

nonn,look


AUTHOR

M. F. Hasler, Jan 16 2015


STATUS

approved



