

A260648


Number of distinct prime divisors p of the nth composite number c such that gpf(c  p) = p, where gpf = greatest prime factor (A006530).


1



1, 2, 0, 1, 2, 1, 1, 2, 0, 1, 1, 2, 1, 0, 1, 1, 1, 1, 2, 0, 1, 2, 2, 0, 1, 2, 0, 1, 1, 1, 1, 0, 1, 1, 2, 1, 0, 2, 1, 2, 1, 0, 1, 1, 0, 2, 2, 1, 1, 1, 0, 1, 1, 1, 2, 1, 1, 0, 1, 1, 2, 1, 1, 1, 0, 2, 1, 1, 1, 2, 0, 0, 2, 0, 1, 1, 2, 1, 0, 1, 2, 1, 1, 1, 1, 1, 1, 2, 0, 1, 1, 1, 1, 1, 0, 0, 1, 3
(list;
graph;
refs;
listen;
history;
text;
internal format)



OFFSET

1,2


COMMENTS

a(n) gives the number of times that the nth composite number occurs in A070229.


LINKS

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


EXAMPLE

a(8) = 2 since the distinct prime divisors of A002808(8) = 15 are 3 and 5, A006530(15  3) = 3 and A006530(15  5) = 5, so all prime 3 and 5 are to be considered.


MAPLE

N:= 1000: # to consider composites <= N
f:= proc(c) local p, t;
if isprime(c) then return NULL fi;
nops(select(p > max(numtheory:factorset(c/p1))<=p, numtheory:factorset(c)))
end proc:
map(f, [$4..N]); # Robert Israel, May 02 2017


CROSSREFS

Cf. A002808 (composite), A006530 (gpf).
Sequence in context: A033781 A141803 A249147 * A127242 A025853 A228247
Adjacent sequences: A260645 A260646 A260647 * A260649 A260650 A260651


KEYWORD

nonn


AUTHOR

Gionata Neri, Nov 12 2015


EXTENSIONS

a(87) corrected by Robert Israel, May 02 2017


STATUS

approved



