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A192861 Flat numbers: odd n such that n+1 is a squarefree number times a power of two. 5

%I

%S 1,3,5,7,9,11,13,15,19,21,23,25,27,29,31,33,37,39,41,43,45,47,51,55,

%T 57,59,61,63,65,67,69,73,75,77,79,81,83,85,87,91,93,95,101,103,105,

%U 109,111,113,115,117,119,121,123,127,129,131,133,135,137,139,141

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

%H Charles R Greathouse IV, <a href="/A192861/b192861.txt">Table of n, a(n) for n = 1..10000</a>

%H Kevin Broughan and Zhou Qizhi, <a href="http://www.math.waikato.ac.nz/~kab/papers/flatandthin4.pdf">Flat primes and thin primes</a>, Bulletin of the Australian Mathematical Society 82:2 (2010), pp. 282-292.

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

%o (PARI) is(n)=n%2&&issquarefree((n+1)>>valuation(n+1,2))

%o (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

%Y Cf. A192862.

%K nonn

%O 1,2

%A _Charles R Greathouse IV_, Jul 11 2011

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Last modified July 23 22:20 EDT 2021. Contains 346265 sequences. (Running on oeis4.)