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 A039786 #6 Mar 11 2014 22:22:58 %S A039786 2,3,5,7,9,11,13,23,29,31,43,47,53,59,61,67,71,79,83,103,107,131,139, %T A039786 149,157,167,173,179,191,211,223,227,229,239,263,269,277,283,293,311, %U A039786 317,331,347,349,359,367,373,383,389,419,421,431,439,443,461,463,467,479 %N A039786 phi(a(n)) is equal to the multiplicative projection of (a(n)-1). %C A039786 Only primes (except 9) may qualify. %H A039786 Charles R Greathouse IV, <a href="/A039786/b039786.txt">Table of n, a(n) for n = 1..10000</a> %e A039786 phi(29)=28, 28=2^2*7^1, 2*2*7*1=28. %o A039786 (PARI) is(n)=my(f=factor(n)); eulerphi(f)==prod(i=1,#f~,f[i,1]*f[i,2])-1 \\ _Charles R Greathouse IV_, Mar 11 2014 %Y A039786 Cf. A000010, A000026. %K A039786 nonn %O A039786 1,1 %A A039786 _Olivier Gérard_ %E A039786 a(1) inserted by _Charles R Greathouse IV_, Mar 11 2014