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 A056773 #10 Apr 28 2020 15:31:19 %S A056773 12,18,24,28,36,40,66,88,124,184,232,328,424,508,664,712,904,1048, %T A056773 1384,1432,1528,1864,1912,2008,2248,2344,2586,2872,3352,3448,3544, %U A056773 3928,4072,4744,5128,5224,5272,5464,5752,5944,6088,6472,7288,7624,8104,8152,8248 %N A056773 Composite n such that phi(n+4) = phi(n)+4. %C A056773 Are all terms even? - _Robert Israel_, Apr 28 2020 %H A056773 Robert Israel, <a href="/A056773/b056773.txt">Table of n, a(n) for n = 1..10000</a> %e A056773 24 is in the sequence because 24 is composite and phi(24)+4 = 12 = phi(24+4). %p A056773 filter:= n -> not isprime(n) and numtheory:-phi(n+4)=numtheory:-phi(n)+4: %p A056773 select(filter, [$1..10000]); # _Robert Israel_, Apr 28 2020 %t A056773 Select[Range[9000],CompositeQ[#]&&EulerPhi[#]+4==EulerPhi[#+4]&] (* _Harvey P. Dale_, Feb 12 2015 *) %o A056773 (PARI) is(n)=!isprime(n) && eulerphi(n+4)==eulerphi(n)+4 \\ _Charles R Greathouse IV_, Apr 28 2020 %Y A056773 A001838, A015913, A055458. Composites in A056772. Primes in A056772 are A023200. %K A056773 nonn %O A056773 1,1 %A A056773 _Labos Elemer_, Aug 17 2000 %E A056773 Edited by _Robert Israel_, Apr 28 2020