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 A056781 #7 Jul 15 2017 11:05:24 %S A056781 2,3,4,5,7,8,9,11,13,16,25,27,32,49,64,81,125,128,243,256,512,625,729, %T A056781 1024,2048,2187,4096,6561,8192,16384,32768,65536 %N A056781 Prime powers such that the 4th power of the number of divisors is not smaller than the number itself. %C A056781 For any integers n, d[n]^4>n should form finite albeit very large sequence. %F A056781 p^w<=(w+1)^4 i.e. p<=(w+1)^(4/w) restricts possible primes and their exponents %e A056781 Equality holds in 12 cases: n=6561=3^8,d[n]=9 and d^4=9^4=3^8=n n=625,d[n]=5, so d^4=n %t A056781 Select[Select[Range[2^16], PrimePowerQ], DivisorSigma[0, #]^4 >= # &] (* _Michael De Vlieger_, Jul 15 2017 *) %Y A056781 A000005, A034884, A035033-A035035. %K A056781 fini,full,nonn %O A056781 1,1 %A A056781 _Labos Elemer_, Aug 18 2000