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 A169730 Write the n-th squarefree semiprime as prime(m)*prime(k). Then a(n) is the absolute value of prime(m)*k-prime(k)*m. 1
 1, 1, 1, 1, 2, 1, 1, 7, 3, 1, 3, 8, 5, 13, 8, 14, 9, 9, 9, 19, 13, 9, 15, 16, 15, 28, 10, 29, 17, 17, 21, 38, 24, 25, 19, 25, 43, 44, 20, 29, 49, 31, 1, 37, 31, 38, 35, 58, 29, 37, 67, 41, 68, 51, 8, 47, 77, 49, 46, 58, 49, 7, 82, 51, 59, 47, 51, 83, 11, 53, 66, 92 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,5 LINKS Table of n, a(n) for n=1..72. EXAMPLE a(1)=1 because prime(1)*2-prime(2)*1=4-3=1; a(2)=1 because prime(1)*3-prime(3)*2=6-5=1. MAPLE A006881 := proc(n) option remember; if n = 1 then 6; else for a from procname(n-1)+1 do if numtheory[bigomega](a)=2 and issqrfree(a) then return a; end if; end do: end if; end proc: A169730 := proc(n) local p, k, pm, pk; p := numtheory[factorset](A006881(n)) ; pm := op(1, p) ; pk := op(2, p) ; k := numtheory[pi](pk) ; m := numtheory[pi](pm) ; abs(pm*k-pk*m) ; end proc: seq(A169730(n), n=1..72) ; # R. J. Mathar, Jun 02 2016 CROSSREFS Cf. A006881. Sequence in context: A301922 A144510 A143670 * A220725 A333142 A196832 Adjacent sequences: A169727 A169728 A169729 * A169731 A169732 A169733 KEYWORD nonn,less AUTHOR Juri-Stepan Gerasimov, Apr 28 2010 EXTENSIONS Corrected by R. J. Mathar, Jun 02 2016 STATUS approved

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Last modified May 23 02:30 EDT 2024. Contains 372758 sequences. (Running on oeis4.)