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 A270779 #22 Sep 08 2022 08:46:16 %S A270779 3,5,7,17,67,257,65537,8942223643 %N A270779 Primes p such that sigma(p-1) + phi(p-1) = (5p-7)/2. %C A270779 Primes p such that A065387(p-1) = (5p-7)/2. %C A270779 Fermat primes from A019434 are terms. %C A270779 Prime terms from A270837. %C A270779 a(9), if it exists, is larger than 10^13. - _Giovanni Resta_, Apr 10 2016 %e A270779 17 is in the sequence because sigma(16)+phi(16) = 31+8 = 39 = (5*17-7)/2. %t A270779 Select[Prime@ Range[10^4], 2 (DivisorSigma[1, # - 1] + EulerPhi[# - 1]) == 5 # - 7 &] (* _Michael De Vlieger_, Mar 24 2016 *) %o A270779 (Magma) [n: n in[1..10^7] | IsPrime(n) and 2*(SumOfDivisors(n-1) + EulerPhi(n-1)) eq 5*n-7] %o A270779 (PARI) lista(nn) = forprime(p=2, nn, if (sigma(p-1) + eulerphi(p-1) == (5*p-7)/2, print1(p, ", "))); \\ _Michel Marcus_, Mar 23 2016 %Y A270779 Cf. A000010, A000203, A065387, A270778, A270837. %K A270779 nonn,more %O A270779 1,1 %A A270779 _Jaroslav Krizek_, Mar 22 2016 %E A270779 a(8) from _Michel Marcus_, Mar 23 2016