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 A039778 #18 Aug 03 2025 03:48:16 %S A039778 32,38,54,56,84,20720 %N A039778 phi(n) is equal to the sum of prime factors and exponents of n+1. %C A039778 a(7) > 10^8. - _Naohiro Nomoto_, Jun 21 2001 %C A039778 a(7) > 10^9. - _Michel Marcus_, Jun 03 2014 %C A039778 a(7) > 10^12. - _Giovanni Resta_, Jun 11 2016 %e A039778 phi(38)=18, 39=3^1*13^1, 3+1+13+1=18. %t A039778 Select[Range[30000], EulerPhi[#] == Plus @@ Flatten@ FactorInteger[# + 1] &] (* _Giovanni Resta_, Jun 11 2016 *) %o A039778 (PARI) isok(n) = (f = factor(n+1)) && (sum(i=1, #f~, f[i,2]) + sum(i=1, #f~, f[i,1]) == eulerphi(n)); \\ _Michel Marcus_, Jun 03 2014 %Y A039778 Cf. A000010, A008474. %K A039778 nonn,more,hard %O A039778 1,1 %A A039778 _Olivier Gérard_