|
| |
|
|
A102820
|
|
Number of primes between 2*p(n) and 2*p(n+1), where p(n) is the n-th prime.
|
|
2
| |
|
|
1, 1, 2, 2, 1, 2, 1, 2, 2, 2, 3, 1, 1, 1, 3, 3, 0, 2, 2, 0, 3, 1, 2, 4, 2, 0, 1, 0, 1, 6, 1, 3, 1, 3, 0, 3, 1, 1, 1, 3, 1, 3, 1, 1, 1, 4, 4, 1, 1, 2, 1, 1, 3, 2, 2, 0, 1, 1, 1, 1, 3, 6, 2, 0, 1, 6, 1, 3, 0, 1, 1, 3, 2, 2, 1, 2, 1, 1, 2, 4, 1, 3, 1, 1, 2, 1, 2, 1, 0, 1, 4, 2, 1, 3, 0, 2, 5, 0, 5, 3, 3, 2, 1, 0, 2
(list; graph; refs; listen; history; internal format)
|
|
|
|
OFFSET
| 1,3
|
|
|
COMMENTS
| Number of primes between successive even semiprimes. [From Juri-Stepan Gerasimov (2stepan(AT)rambler.ru), May 01 2010]
|
|
|
LINKS
| V. Shevelev, On critical small intervals containing primes [From Vladimir Shevelev (shevelev(AT)bgu.ac.il), Aug 24 2009]
|
|
|
EXAMPLE
| a(15)=3 because there are 3 primes between the doubles of the 15th and 16th primes, that is between 2*47 and 2* 53.
|
|
|
MATHEMATICA
| MyA102820=Table[PrimePi[2 Prime[n+1]]-PrimePi[2 Prime[n]], {n, 150}] (Seidov)
f[n_] := PrimePi[2Prime[n + 1]] - PrimePi[2Prime[n]]; Table[ f[n], {n, 105}] (from Robert G. Wilson v Mar 03 2005)
|
|
|
CROSSREFS
| Cf. A104380.
A104272 A080359 [From Vladimir Shevelev (shevelev(AT)bgu.ac.il), Aug 24 2009]
Sequence in context: A091267 A003643 A058062 * A024317 A024880 A029424
Adjacent sequences: A102817 A102818 A102819 * A102821 A102822 A102823
|
|
|
KEYWORD
| easy,nonn
|
|
|
AUTHOR
| Ali A. Tanara (tanara(AT)khayam.ut.ac.ir), Feb 27 2005
|
|
|
EXTENSIONS
| More terms from Zak Seidov (zakseidov(AT)yahoo.com), Feb 28 2005
|
| |
|
|
