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 A304253 #8 May 09 2018 23:04:18 %S A304253 20,68,76,92,8248 %N A304253 Numbers k such that k = Product (p_j^e_j) = Sum (prime(p_j)^e_j). %C A304253 Fixed points of A304251. %H A304253 <a href="/index/Pri#prime_indices">Index entries for sequences computed from indices in prime factorization</a> %e A304253 68 is a term because 68 = 2^2*17 = prime(1)^2*prime(7) = prime(prime(1))^2 + prime(prime(7)). %e A304253 8248 is a term because 8248 = 2^3*1031 = prime(1)^3*prime(173) = prime(prime(1))^3 + prime(prime(173)). %t A304253 a[n_] := Plus @@ (Prime[#[[1]]]^#[[2]] & /@ FactorInteger[n]); Select[Range[10000], a[#] == # &] %o A304253 (PARI) isok(n) = my(f=factor(n)); n == sum(k=1, #f~, prime(f[k,1])^f[k,2]); \\ _Michel Marcus_, May 09 2018 %Y A304253 Cf. A006450, A008478, A048768, A304194, A304251. %K A304253 nonn,more %O A304253 1,1 %A A304253 _Ilya Gutkovskiy_, May 09 2018