A074810 Number of primes between n and 2n (inclusive) = largest prime factor of n.

1, 2, 4, 8, 9, 28, 65, 114, 174, 186, 246, 623, 1784, 1832, 1912, 5121, 13810, 14090, 39413, 40403, 808822, 809858, 810026, 2201505, 2202735, 6047408, 6048656, 16463939, 16467271, 16472371, 121482371, 121495747, 330358060, 898100679

Offset

1,2

Links

Table of n, a(n) for n=1..34.

Example

a(6) = 28 because there are 7 primes between n = 28 and 2n = 56: 29, 31, 37, 41, 43, 47, 53; and the largest prime dividing 28 is 7.

Maple

with(numtheory): a:=proc(n) if pi(2*n)-pi(n-1)=factorset(n)[nops(factorset(n))] then n else fi end: 1, seq(a(n), n=2..1000); # Emeric Deutsch, Feb 05 2006

Crossrefs

Cf. A006530, A035250.

Sequence in context: A140141 A088274 A118418 * A028984 A294369 A302907

Adjacent sequences: A074807 A074808 A074809 * A074811 A074812 A074813

Keyword

nonn

Author

Jason Earls, Sep 08 2002

Extensions

More terms from Emeric Deutsch, Feb 05 2006

a(24)-a(34) from Donovan Johnson, Apr 23 2010

Status

approved