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 A176539 Indices of nonprime numbers in the products of two noncomposite numbers. 1
 1, 4, 6, 8, 9, 12, 13, 16, 17, 19, 20, 23, 24, 25, 27, 28, 31, 33, 34, 36, 37, 38, 41, 42, 44, 47, 48, 50, 52, 53, 54, 56, 57, 58, 59, 63, 66, 68, 69, 70, 71, 72, 73, 75, 77, 78, 81, 82, 83, 84, 85, 88, 90, 91, 92, 94, 96, 98, 99, 102, 103, 104, 107, 110, 111, 112, 113, 114 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS The positions of nonprime numbers in A037143. The nonprime numbers A018252 which are not in A037143 do not contribute to the sequence and have no index of this kind. - R. J. Mathar, May 01 2010 LINKS MAPLE From R. J. Mathar, May 01 2010: (Start) A037143 := proc(n) option remember; if n = 1 then 1; else for a from procname(n-1)+1 do if numtheory[bigomega](a) <=2 then return a; end if; end do: end if; end proc: A018252 := proc(n) option remember; if n = 1 then 1; else for a from procname(n-1)+1 do if not isprime(a) then return a; end if; end do: end if; end proc: A176539 := proc(n) npr := A018252(n) ; for a from 1 do if A037143(a) = npr then return a ; elif A037143(a) > npr then return ; end if; end do: end proc: seq(A176539(n), n=1..220) ; (End) CROSSREFS Cf. A018252. Sequence in context: A338461 A163520 A273546 * A285256 A013920 A179891 Adjacent sequences:  A176536 A176537 A176538 * A176540 A176541 A176542 KEYWORD nonn AUTHOR Juri-Stepan Gerasimov, Apr 19 2010 EXTENSIONS Corrected (70 inserted) by R. J. Mathar, May 01 2010 STATUS approved

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Last modified April 13 21:13 EDT 2021. Contains 342941 sequences. (Running on oeis4.)