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 A329025 #7 Nov 04 2019 09:22:39
%S A329025 0,1,2,1,3,12,4,1,2,13,5,12,6,14,23,1,7,12,8,13,24,15,9,12,3,16,2,14,
%T A329025 10,123,11,1,25,17,34,12,12,18,26,13,13,124,14,15,23,19,15,12,4,13,27,
%U A329025 16,16,12,35,14,28,110,17,123,18,111,24,1,36,125,19,17,29,134
%N A329025 If n = Product (p_j^k_j) then a(n) = concatenation (pi(p_j)), where pi = A000720.
%C A329025 Concatenate of indices of distinct prime factors of n, in increasing order.
%H A329025 Ilya Gutkovskiy, <a href="/A329025/a329025.jpg">Scatter plot of a(n) up to n=100000</a>
%H A329025 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a>
%F A329025 a(prime(n)^k) = n for k > 0.
%e A329025 a(60) = a(2^2 * 3 * 5) = a(prime(1)^2 * prime(2) * prime(3)) = 123.
%t A329025 a[n_] := FromDigits[Flatten@IntegerDigits@(PrimePi[#[[1]]] & /@ FactorInteger[n])]; Table[a[n], {n, 1, 70}]
%Y A329025 Cf. A000720, A037916, A080695, A084317, A127668, A304038, A329026.
%K A329025 nonn,base
%O A329025 1,3
%A A329025 _Ilya Gutkovskiy_, Nov 02 2019