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 A005073 #18 Jun 21 2022 05:09:07 %S A005073 0,0,0,0,0,0,2401,0,0,0,0,0,28561,2401,0,0,0,0,130321,0,2401,0,0,0,0, %T A005073 28561,0,2401,0,0,923521,0,0,0,2401,0,1874161,130321,28561,0,0,2401, %U A005073 3418801,0,0,0,0,0,2401,0,0,28561,0,0,0,2401,130321,0,0,0,13845841,923521,2401,0,28561,0,20151121,0,0,2401,0,0,28398241,1874161 %N A005073 Sum of 4th powers of primes = 1 mod 3 dividing n. %H A005073 Antti Karttunen, <a href="/A005073/b005073.txt">Table of n, a(n) for n = 1..10001</a> %F A005073 Additive with a(p^e) = p^4 if p = 1 (mod 3), 0 otherwise. %t A005073 f[p_, e_] := If[Mod[p, 3] == 1, p^4, 0]; a[n_] := Plus @@ f @@@ FactorInteger[n]; a[1] = 0; Array[a, 100] (* _Amiram Eldar_, Jun 21 2022 *) %o A005073 (Scheme) (define (A005073 n) (if (= 1 n) 0 (+ (A000583 (if (= 1 (modulo (A020639 n) 3)) (A020639 n) 0)) (A005073 (A028234 n))))) ;; _Antti Karttunen_, Jul 09 2017 %o A005073 (PARI) a(n) = my(f=factor(n)); sum(k=1, #f~, if (((p=f[k,1])%3) == 1, p^4)); \\ _Michel Marcus_, Jul 10 2017 %Y A005073 Cf. A000583, A005070, A005071, A005072. %K A005073 nonn %O A005073 1,7 %A A005073 _N. J. A. Sloane_ %E A005073 More terms from _Antti Karttunen_, Jul 09 2017