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 A381491 #17 Feb 27 2025 10:48:48
%S A381491 0,1,2,3,4,5,6,7,8,9,9,2,4,8,9,7,9,2,4,8,9,5,2,9,7,4,8,9,2,9,4,8,7,9,
%T A381491 5,2,9,4,8,9,7,2,4,9,8,9,2,4,5,9,7,8,9,2,4,9,8,7,9,2,4,8,9,5,9,2,7,4,
%U A381491 8,9,9,2,4,8,9,7,5,9,2,4,8,9,7,2,9,4,8,9
%N A381491 a(n) = A010888(A381487(n)).
%H A381491 Michel Marcus, <a href="/A381491/b381491.txt">Table of n, a(n) for n = 1..3347</a>
%e A381491 a(12) = 2 because the digital root of A381487(12) = 128 is 2.
%t A381491 A010888[n_]:=n - 9*Floor[(n-1)/9]; kmax=5*10^6; a={0,1}; For[k=2, k<=kmax, k++, If[A010888[k]!=1, If[IntegerQ[Log[A010888[k],k]], AppendTo[a,A010888[k]]]]]; a
%o A381491 (PARI) dr(n) = if(n, (n-1)%9+1); \\ A010888
%o A381491 lista(nn) = my(list = List()); listput(list, 0); listput(list, 1); for (n=2, 9, for (k=1, logint(nn, n), if (dr(n^k) == n, listput(list, n^k)););); apply(x->dr(x), vecsort(Vec(list))); \\ _Michel Marcus_, Feb 27 2025
%Y A381491 Cf. A010888, A381487, A381492.
%K A381491 nonn,base
%O A381491 1,3
%A A381491 _Stefano Spezia_, Feb 25 2025
%E A381491 More terms from _Michel Marcus_, Feb 27 2025