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A192861 Flat numbers: odd n such that n+1 is a squarefree number times a power of two. 5
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 (list; graph; refs; listen; history; text; internal format)
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 * A192868 A283553 A081110

Adjacent sequences:  A192858 A192859 A192860 * A192862 A192863 A192864

KEYWORD

nonn

AUTHOR

Charles R Greathouse IV, Jul 11 2011

STATUS

approved

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Last modified November 19 03:40 EST 2019. Contains 329310 sequences. (Running on oeis4.)