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 A289690 #24 Mar 14 2021 18:45:57 %S A289690 5,1,2,12,0 %N A289690 Least k such that there are exactly n perfect powers between 10k and 10k + 10. %C A289690 I do not know if a(5) exists. If it does, the numbers 10k+1, 10k+3, 10k+5, 10k+7, 10k+9 will be perfect powers. But those numbers are very scarce. %C A289690 Further, a(6), ..., a(10) cannot exist because of the Mihailescu theorem, as the only adjoining perfect powers are 8 and 9. %C A289690 a(5) is extremely unlikely to exist; if it does, it is larger than 10^70. - _Charles R Greathouse IV_, Jul 21 2017 %e A289690 If n=2, then there are 2 power numbers between 20 and 30: 25 and 27, and this is the least k with this property. %o A289690 (PARI) a(n)=my(k=0); while(sum(j=10*k+1, 10*k+9, (j==1) || ispower(j)) !=n, k++); k; \\ _Michel Marcus_, Jul 20 2017 %Y A289690 Cf. A001597, A097056. %K A289690 nonn,fini %O A289690 0,1 %A A289690 _Wolfram Hüttermann_, Jul 09 2017