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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

Table of n, a(n) for n=1..68.

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: A068631 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 March 22 17:25 EDT 2019. Contains 321422 sequences. (Running on oeis4.)