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A074810
Number of primes between n and 2n (inclusive) = largest prime factor of n.
0
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
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
Sequence in context: A140141 A088274 A118418 * A028984 A294369 A302907
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