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%I #6 Oct 04 2015 01:47:49
%S 2,5,7,11,17,23,19,31,23,43,59,31,67,47,71,73,79,83,59,89,53,107,109,
%T 113,127,131,89,137,139,97,149,103,157,163,167,173,179,181,127,191,
%U 131,197,199,223,151,227,22,9,233,239,241,163,263,271,181,277,281,283,293
%N Primes of the form n/2*(c(n)-r(n)), where c(n)=n-th composite and r(n)=n-th nonprime.
%e If n=12, then 12/2*(c(12)-r(12))=6/(21-18)=2=a(1).
%e If n=30, then 30/2*(c(30)-r(30))=15/(45-42)=5=a(2).
%e If n=42, then 42/2*(c(42)-r(42))=21/(60-57)=7=a(3).
%e If n=66, then 66/2*(c(66)-r(66))=33/(91-88)=11=a(4).
%e If n=68, then 68/2*(c(68)-r(68))=34/(93-91)=17=a(5), etc.
%p A141468 := proc(n) option remember ; if n = 1 then 0; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: A002808 := proc(n) option remember ; A141468(n+2) ; end: for n from 1 to 3000 do p := n/(A002808(n)-A141468(n))/2 ; if type(p,'integer') then if isprime(p) then printf("%d,",p) ; fi; fi; od: # _R. J. Mathar_, Jan 23 2009
%Y Cf. A002808, A141468.
%K nonn
%O 1,1
%A _Juri-Stepan Gerasimov_, Sep 21 2008
%E Corrected and extended by _R. J. Mathar_, Jan 23 2009
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