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Search: id:A122121
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| A122121 |
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Number of primes <= 10^(n/2). |
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+0
15
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| 0, 2, 4, 11, 25, 65, 168, 446, 1229, 3401, 9592, 27293, 78498, 227647, 664579, 1951957, 5761455, 17082666
(list; graph; listen)
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OFFSET
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0,2
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FORMULA
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a(2n)=A006880(n). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 13 2007
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EXAMPLE
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a(3) = 11: sqrt(1000) = 31.62277660..., pi(31) = 11.
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PROGRAM
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(PARI) { a= 0; n= 1; p=2 ; while(1, a++ ; pnext =nextprime(p+1) ; if( p^2 <= 10^n && pnext^2>10^n, print(a) ; n++ ; ) ; p=pnext ; ) ; } - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 13 2007
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CROSSREFS
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Cf. A000720, A006880.
Sequence in context: A100550 A071973 A086424 this_sequence A080009 A159336 A151257
Adjacent sequences: A122118 A122119 A122120 this_sequence A122122 A122123 A122124
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KEYWORD
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nonn,more
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com), based on a suggestion from Klaus Kastberg (Kastberg(AT)aapt.net.au), Oct 17 2006
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EXTENSIONS
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More terms from R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jan 13 2007
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