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 A260648 Number of distinct prime divisors p of the n-th 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 n-th 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/p-1))<=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 A325392 A025853 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

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Last modified February 21 20:46 EST 2020. Contains 332111 sequences. (Running on oeis4.)