A192861 Flat numbers: odd n such that n+1 is a squarefree number times a power of two.

1, 3, 5, 7, 9, 11, 13, 15, 19, 21, 23, 25, 27, 29, 31, 33, 37, 39, 41, 43, 45, 47, 51, 55, 57, 59, 61, 63, 65, 67, 69, 73, 75, 77, 79, 81, 83, 85, 87, 91, 93, 95, 101, 103, 105, 109, 111, 113, 115, 117, 119, 121, 123, 127, 129, 131, 133, 135, 137, 139, 141

Offset

1,2

Links

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

Kevin Broughan and Zhou Qizhi, Flat primes and thin primes, Bulletin of the Australian Mathematical Society 82:2 (2010), pp. 282-292.

Formula

a(n) ~ Pi^2/4 * n.

Prog

(PARI) is(n)=n%2&&issquarefree((n+1)>>valuation(n+1, 2))
(PARI) list(lim)=my(v=List()); for(k=1, logint(1+lim\=1, 2), forsquarefree(n=1, (lim+1)>>k, listput(v, n[1]<<k-1))); Set(v) \\ Charles R Greathouse IV, Mar 01 2018

Crossrefs

Cf. A192862.

Sequence in context: A294923 A005842 A204458 * A333854 A192868 A283553

Adjacent sequences: A192858 A192859 A192860 * A192862 A192863 A192864

Keyword

nonn

Author

Charles R Greathouse IV, Jul 11 2011

Status

approved