OFFSET
1,2
EXAMPLE
1st composite=4=2*2=prime(1)*prime(1) and 1+1=2 prime, so a(1)=1.
2nd composite=6=2*3=prime(1)*prime(2) and 1+2=3 prime, so a(2)=2.
3rd composite=8=2*2*2=prime(1)*prime(1)*prime(1) and 1+1+1=3 prime, so a(3)=3.
7th composite=14=2*7=prime(1)*prime(4) and 1+4=5 prime, so a(4)=7.
MAPLE
A056239 := proc(n) pfs := ifactors(n)[2] ; add ( op(2, d)*numtheory[pi](op(1, d)), d=pfs) ; end: A002808 := proc(n) option remember ; if n = 1 then 4; else for a from procname(n-1)+1 do if not isprime(a) then RETURN(a) ; fi; od: fi; end: for n from 1 to 300 do if isprime(A056239( A002808(n))) then printf("%d, ", n) ; fi; od: # R. J. Mathar, Aug 01 2009
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, Jul 30 2009
EXTENSIONS
Values from a(16) on corrected by R. J. Mathar, Aug 01 2009
STATUS
approved