OFFSET
1,1
EXAMPLE
If n=12, then 12/2*(c(12)-r(12))=6/(21-18)=2=a(1).
If n=30, then 30/2*(c(30)-r(30))=15/(45-42)=5=a(2).
If n=42, then 42/2*(c(42)-r(42))=21/(60-57)=7=a(3).
If n=66, then 66/2*(c(66)-r(66))=33/(91-88)=11=a(4).
If n=68, then 68/2*(c(68)-r(68))=34/(93-91)=17=a(5), etc.
MAPLE
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
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Sep 21 2008
EXTENSIONS
Corrected and extended by R. J. Mathar, Jan 23 2009
STATUS
approved