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 A072303 #8 Dec 29 2013 22:03:12 %S A072303 1,2,3,4,5,6,7,8,9,11,12,13,16,17,18,19,21,23,24,25,27,28,29,31,32,36, %T A072303 37,41,43,47,48,49,53,54,59,61,64,67,71,72,73,79,81,83,89,96,97,101, %U A072303 103,107,108,109,112,113,121,125,127,128,131,137,139,144,149,151,157 %N A072303 Numbers n for which n is congruent to n^2 mod phi(n). %C A072303 Or, numbers n such that phi(n) divides n*(n-1). - Mohammed Bouayoun (mohammed.bouayoun(AT)sanef.com), Apr 14 2006 %H A072303 Charles R Greathouse IV, <a href="/A072303/b072303.txt">Table of n, a(n) for n = 1..10000</a> %e A072303 9 is in the sequence because phi(9) = 6. 9 % 6 = 3 and 9^2 % 6 = 3. But 10 is not in the sequence because phi(10) = 4 and 10 % 4 = 6 and 10^2 % 4 = 0. %o A072303 (PARI) isok(n) = ((n^2 - n) % eulerphi(n)) == 0 \\ _Michel Marcus_, Jun 07 2013 %Y A072303 Cf. A000010, A068494. %K A072303 easy,nonn %O A072303 1,2 %A A072303 Igor Naverniouk (igor(AT)lexansoft.com), Jul 14 2002