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A063638
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Primes p such that p-2 is a semiprime.
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7
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11, 17, 23, 37, 41, 53, 59, 67, 71, 79, 89, 97, 113, 131, 157, 163, 179, 211, 223, 239, 251, 269, 293, 307, 311, 331, 337, 367, 373, 379, 383, 397, 409, 419, 439, 449, 487, 491, 499, 503, 521, 547, 593, 599, 613, 631, 673, 683, 691, 701, 709, 719, 733, 739
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Primes of form p*q + 2, where p and q are primes.
11 is the only prime of this form where p=q. For prime p>3, 3 divides p^2+2. - T. D. Noe (noe(AT)sspectra.com), Mar 01 2006
The asymptotic growth of this sequence is relevant for A204142. We have a(10^k) = (11, 79, 1571, 27961, 407741, 5647823, ...). - M. F. Hasler, Feb 13 2012
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LINKS
| M. F. Hasler, Table of n, a(n) for n = 1..10000
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MATHEMATICA
| Take[Select[ # + 2 & /@ Union[Flatten[Outer[Times, Prime[Range[100]], Prime[Range[100]]]]], PrimeQ], 60]
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PROG
| (PARI) { n=0; for (m=2, 10^9, p=prime(m); if (bigomega(p - 2) == 2, write("b063638.txt", n++, " ", p); if (n==1000, break)) ) } [From Harry J. Smith (hjsmithh(AT)sbcglobal.net), Aug 26 2009]
(PARI) forprime(p=3, 9999, bigomega(p-2)==2 & print1(p", "))
(PARI) p=2; for(n=1, 1e4, until(bigomega(-2+p=nextprime(p+1))==2, ); write("b063638.txt", n" "p)) \\ - M. F. Hasler, Feb 13 2012
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CROSSREFS
| Cf. A005385, A001358, A063637.
Cf. A109611 (Chen primes).
Cf. A204142.
Sequence in context: A066938 A076812 A074207 * A141250 A096454 A099722
Adjacent sequences: A063635 A063636 A063637 * A063639 A063640 A063641
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KEYWORD
| nonn,changed
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AUTHOR
| Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Jul 21 2001
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