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 A307587 #13 Apr 19 2019 18:37:52 %S A307587 1,2,190,280,480,1073,1674,1736,4850,15867,16230,16302,23715,24056, %T A307587 25064,35712,52976,54730,75184,105342,456382,964325 %N A307587 Numbers k such that the determinant of the Vandermonde matrix of their digits is equal to phi(k), the Euler totient function of k. %C A307587 Tested all the 8877691 numbers with distinct digits; no additional terms. - _Giovanni Resta_, Apr 16 2019 %e A307587 | 1 1 1 | %e A307587 det | 1 9 81 | = 72 = phi(190). %e A307587 | 1 0 0 | %p A307587 with(numtheory): with(linalg): P:=proc(q) local a,c,k,n; %p A307587 for n from 1 to q do a:=convert(n,base,10): c:=[]: %p A307587 for k from 1 to nops(a) do c:=[op(c), a[-k]]; od; %p A307587 if phi(n)=det(vandermonde(c)) then print(n); fi; od; end: P(10^9); %Y A307587 Cf. A000005, A307586. %K A307587 nonn,base,fini,full %O A307587 1,2 %A A307587 _Paolo P. Lava_, Apr 16 2019