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 A131284 Numbers n such that difference between prime factors of n-th semiprime is n. 3
 5, 80, 86, 613668, 6384425704 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The 6384425704th semiprime is 44690979977 = 7*6384425711. 6384425711 - 7 = 6384425704. - Donovan Johnson, Jul 11 2010 LINKS EXAMPLE sp(5) = 14 = 2*7 and 7 - 2 = 5, sp(80) = 249 = 3*83 and 83 - 3 = 80, sp(86) = 267 = 3*89 and 89 - 3 = 86; sp(n) = n-th semiprime. PROG (PARI) { n=0; j=1; /* n=3068365-1; j=613668; */ while( l=(j\10^4+1)*10^4, until( l < j++, until(bigomega(n+=1)==2, ); if(2!=#f=factor(n)[, 1], next); if(j==f[2]-f[1], print("\n", [j, n, f]))); print1(j-1, ":"n", "))} \\ M. F. Hasler, Sep 28 2007 CROSSREFS Cf. A064910, A084126, A084127, A109313. Sequence in context: A141828 A134531 A062250 * A105917 A269792 A144344 Adjacent sequences:  A131281 A131282 A131283 * A131285 A131286 A131287 KEYWORD more,nonn AUTHOR Zak Seidov, Sep 25 2007 EXTENSIONS a(4) = 613668 (p=5, q=613673) from M. F. Hasler, Sep 28 2007 a(5) from Donovan Johnson, Jul 11 2010 STATUS approved

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Last modified October 19 07:21 EDT 2018. Contains 316337 sequences. (Running on oeis4.)