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 A116001 #4 Mar 18 2013 12:39:27 %S A116001 6,10,18,20,22,27,34,40,49,52,58,64,68,82,98,100,118,136,142,144,148, %T A116001 160,162,164,202,212,214,242,243,244,274,288,289,298,320,325,333,338, %U A116001 343,356,358,361,382,392,394,404,436,441,454,464,478,512,538,544,548 %N A116001 sigma(n) - phi(n) gives a semiprime (A001358). %H A116001 Harvey P. Dale, <a href="/A116001/b116001.txt">Table of n, a(n) for n = 1..1000</a> %e A116001 sigma(100)-phi(100)=177=3*59 %t A116001 Select[Range[600],PrimeOmega[DivisorSigma[1,#]-EulerPhi[#]]==2&] (* _Harvey P. Dale_, Mar 18 2013 *) %Y A116001 Cf. A001358, A116017, A116000. %K A116001 nonn %O A116001 1,1 %A A116001 _Giovanni Resta_, Feb 13 2006