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A177997
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p and A002808(p)/2 are both prime.
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1
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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
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OFFSET
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1,1
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COMMENTS
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Primes p such that composite(p) is an even semiprime.
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LINKS
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Robert Israel, Table of n, a(n) for n = 1..10000
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EXAMPLE
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a(1)=2 because 2=prime and composite(2)/2=6/2=3=prime.
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MAPLE
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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
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PROG
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(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
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CROSSREFS
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Cf. A002808, A065858, A065897.
Sequence in context: A250173 A038945 A215210 * A238776 A141112 A053647
Adjacent sequences: A177994 A177995 A177996 * A177998 A177999 A178000
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KEYWORD
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nonn
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AUTHOR
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Juri-Stepan Gerasimov, May 17 2010, May 23 2010
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EXTENSIONS
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Corrected by D. S. McNeil and R. J. Mathar, May 23 2010
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STATUS
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approved
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