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 A087247 #22 Jul 09 2018 21:21:13 %S A087247 1,10,14,15,21,22,26,33,34,35,38,39,46,51,55,57,58,62,65,69,74,77,82, %T A087247 85,86,87,91,93,94,95,105,106,110,111,115,118,119,122,123,129,130,133, %U A087247 134,141,142,143,145,146,154,155,158,159,161,165,166,170,177,178,182,183 %N A087247 Squarefree deficient nonprime numbers. %H A087247 Enrique Pérez Herrero, <a href="/A087247/b087247.txt">Table of n, a(n) for n = 1..10000</a> %e A087247 105 = 3*5*7 and sigma(105) = 1 + 3 + 5 + 7 + 15 + 21 + 35 + 105 = 192 < 210 = 2*105, so 105 is in the sequence. %e A087247 The sequence differs from A006881: first term with 3 distinct prime factors is 105. %t A087247 isA087247[n_] := SquareFreeQ[n] && !PrimeQ[n] && (DivisorSigma[1, n] < 2n); Select[Range[200], isA087247] (* _Enrique Pérez Herrero_, Jan 13 2011 *) %o A087247 (PARI) isok(n) = !isprime(n) && issquarefree(n) && (sigma(n) < 2*n); \\ _Michel Marcus_, Jul 09 2018 %Y A087247 Cf. A087244, A087245, A087246, A087248. %Y A087247 Cf. A008683, A000203, A013929, A005117, A005100, A005101. %K A087247 nonn %O A087247 1,2 %A A087247 _Labos Elemer_, Sep 05 2003