The OEIS is supported by the many generous donors to the OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A177997 p and A002808(p)/2 are both prime. 1
 2, 5, 7, 13, 31, 41, 43, 59, 101, 107, 127, 137, 149, 199, 239, 277, 359, 389, 479, 613, 743, 757, 809, 829, 937, 991, 1031, 1103, 1439, 1487, 1499, 1847, 1877, 2011, 2083, 2179, 2609, 2663, 2711, 2741, 2749, 2857, 2909, 3329, 3559, 3623, 3643, 3697, 3823 (list; graph; refs; listen; history; text; internal format)
 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 Cf. A002808, A065858, A065897. Sequence in context: A250173 A038945 A215210 * A238776 A141112 A053647 Adjacent sequences: A177994 A177995 A177996 * A177998 A177999 A178000 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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified March 24 18:34 EDT 2023. Contains 361510 sequences. (Running on oeis4.)