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 A075308 #21 Aug 13 2024 11:21:02 %S A075308 4,8,28,84,242,744,2284,7096,22179,69561,218759,689206,2173942, %T A075308 6862783,21676671,68493153,216477260,684309327,2163434093,6840212693, %U A075308 21628140126,68388775913,216252650605,683825838922,2162393136881,6837971108286,21623312527390,68378377967873 %N A075308 Number of n-digit perfect powers. %F A075308 a(n) = A070428(n) - A070428(n-1) for n >= 3. %e A075308 a(2) = 8 because there are eight 2-digit perfect powers: 16, 25, 27, 32, 36, 49, 64, 81. %e A075308 a(3) = 28 = A070428(3) - A070428(2) = 41 - 13 (in A070428 offset is 0). %o A075308 (Python) %o A075308 from sympy import mobius, integer_nthroot %o A075308 def A075308(n): return int(sum(mobius(x)*(integer_nthroot(10**(n-1),x)[0]-integer_nthroot(10**n,x)[0]) for x in range(2,((10**(n-1)).bit_length())))-sum(mobius(x)*(integer_nthroot(10**n,x)[0]-1) for x in range((10**(n-1)).bit_length(),(10**n).bit_length()))) if n>2 else n<<2 # _Chai Wah Wu_, Aug 13 2024 %Y A075308 Cf. A001597, A070428. %K A075308 nonn,base,easy %O A075308 1,1 %A A075308 _Zak Seidov_, Oct 11 2002 %E A075308 More terms from _Jinyuan Wang_, Mar 02 2020