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 A067350 #14 Aug 13 2019 11:23:22 %S A067350 3,5,6,7,10,11,13,16,17,19,22,23,25,27,29,31,37,40,41,43,46,47,52,53, %T A067350 58,59,61,64,67,68,71,72,73,79,80,82,83,89,97,98,101,103,106,107,109, %U A067350 113,117,127,128,131,136,137,139,144,149,151,157,162,163,166,167,169 %N A067350 Numbers n such that sigma(n)+phi(n) has exactly 4 divisors. %C A067350 For all terms up to 10^12, sigma(n)+phi(n) is a product of 2 distinct primes. The only other possibility is that sigma(n)+phi(n) is a cube of a prime, for some n which is either a square or twice a square; does this occur? If not, then this sequence is contained in A067351. %H A067350 Amiram Eldar, <a href="/A067350/b067350.txt">Table of n, a(n) for n = 1..10000</a> %F A067350 A000005(A000010(n) + A000203(n)) = A067349(n) = 4. %e A067350 Includes all odd primes and some composites; e.g. 22 and 25, since sigma(22)+phi(22)=36+10=46=2*23 and sigma(25)+phi(25)=31+20=51=3*17. %t A067350 Select[ Range[ 1, 200 ], DivisorSigma[ 0, DivisorSigma[ 1, # ]+EulerPhi[ # ] ]==4& ] %o A067350 (PARI) isok(n) = numdiv(sigma(n)+eulerphi(n)) == 4; \\ _Michel Marcus_, Aug 13 2019 %Y A067350 Cf. A000005, A000010, A000203, A067349, A067351. %K A067350 nonn %O A067350 1,1 %A A067350 _Labos Elemer_, Jan 17 2002 %E A067350 Edited by _Dean Hickerson_, Jan 20 2002