This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A192861 #15 May 15 2025 08:18:40 %S A192861 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 A192861 57,59,61,63,65,67,69,73,75,77,79,81,83,85,87,91,93,95,101,103,105, %U A192861 109,111,113,115,117,119,121,123,127,129,131,133,135,137,139,141 %N A192861 Flat numbers: odd n such that n+1 is a squarefree number times a power of two. %H A192861 Charles R Greathouse IV, <a href="/A192861/b192861.txt">Table of n, a(n) for n = 1..10000</a> %H A192861 Kevin Broughan and Zhou Qizhi, <a href="https://doi.org/10.1017/S0004972710000067">Flat primes and thin primes</a>, Bulletin of the Australian Mathematical Society 82:2 (2010), pp. 282-292. %F A192861 a(n) ~ Pi^2/4 * n. %o A192861 (PARI) is(n)=n%2&&issquarefree((n+1)>>valuation(n+1,2)) %o A192861 (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 A192861 Cf. A192862. %K A192861 nonn %O A192861 1,2 %A A192861 _Charles R Greathouse IV_, Jul 11 2011