A141635 - OEIS

%I #4 Mar 30 2012 18:52:27

%S 1,1,1,9,9,49,91,95,35,115,117,69,143,147,159,87,25,95,195,69,215,75,

%T 57,243,249,129,265,267,135,279,35,153,39,105,161,323,329,69,117,363,

%U 387,105,423,429,217,435,437,147,225,153,93,243,245,249,125,515,87,525,527,177

%N Odd nonprimes of the form j/(p(j+1)-p(j)), where p(j)=j-th prime.

%C The nonprimes are listed in order of increasing j, duplicates retained.

%e If j=1, then 1/(p(1+1)-p(1))=1/(3-2)=1=a(1).

%e If j=2, then 2/(p(2+1)-p(2))=2/(5-3)=1=a(2).

%e If j=4, then 4/(p(4+1)-p(4))=4/(11-7)=1=a(3).

%e If j=54, then 54/(p(54+1)-p(54))=54/(257-251)=9=a(4).

%e If j=72, then 72/(p(72+1)-p(72))=72/(367-359)=9=a(5).

%e If j=98, then 98/(p(98+1)-p(98))=98/(523-521)=49=a(6).

%p A141635 := proc() local n,p,p1,q ; n := 1 ; p := ithprime(n); p1 := nextprime(p) ; for n from 1 to 2000 do if n mod (p1-p) = 0 then q := n/(p1-p) ; if not isprime(q) and (q mod 2) = 1 then printf("%d,", q) ; fi; fi; p := p1 ; p1 := nextprime(p1) ; od: RETURN() ; end: A141635() ; # _R. J. Mathar_, Sep 13 2008

%Y Cf. A000040, A141468, A001223.

%K nonn,less

%O 1,4

%A _Juri-Stepan Gerasimov_, Sep 12 2008

%E Corrected from 7th entry on by _R. J. Mathar_, Sep 13 2008