OFFSET
1,1
COMMENTS
Primes p such that composite(p) is an even semiprime.
LINKS
Robert Israel, Table of n, a(n) for n = 1..10000
EXAMPLE
a(1)=2 because 2=prime and composite(2)/2=6/2=3=prime.
MAPLE
P, C:= selectremove(isprime, [$2..10000]):
select(t -> t <= nops(C) and C[t]::even and isprime(C[t]/2), P); # Robert Israel, Mar 20 2018
PROG
(PARI)
c=[]; for(n=2, 10000, if(!isprime(n), c=concat(c, n))); c; \\ The composites
s=[]; forprime(p=2, #c, if(c[p]%2==0 && isprime(c[p]\2), s=concat(s, p))); s \\ Colin Barker, Jun 28 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Juri-Stepan Gerasimov, May 17 2010, May 23 2010
EXTENSIONS
Corrected by D. S. McNeil and R. J. Mathar, May 23 2010
STATUS
approved