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 A115919 #11 Jul 15 2021 21:25:40 %S A115919 2,3,4,5,7,8,9,11,13,16,17,19,23,25,29,31,32,36,37,41,43,47,50,53,59, %T A115919 61,67,71,73,79,81,83,89,97,101,103,107,109,113,121,127,128,131,137, %U A115919 139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,225,227 %N A115919 Numbers k such that sigma(k) - phi(k) is a prime number. %H A115919 Charles R Greathouse IV, <a href="/A115919/b115919.txt">Table of n, a(n) for n = 1..10000</a> %e A115919 sigma(81) - phi(81) = 67, a prime. %t A115919 Select[Range[300],PrimeQ[DivisorSigma[1,#]-EulerPhi[#]]&] (* _Harvey P. Dale_, Feb 25 2011 *) %o A115919 (PARI) is(n)=isprime(sigma(n)-eulerphi(n)) \\ _Charles R Greathouse IV_, Nov 27 2013 %Y A115919 Cf. A038344. %K A115919 nonn %O A115919 1,1 %A A115919 _Giovanni Resta_, Feb 06 2006