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 A157986 #12 Oct 05 2024 22:15:25
%S A157986 2,-2,-3,-2,-4,-2,-3,-5,2,-2,-6,-4,2,-2,-3,-7,2,-2,2,3,2,-5,-8,-2,2,
%T A157986 -3,-2,2,2,2,-9,-2,2,-4,2,-6,2,-2,2,-2,3,-10,2,2,2,4,-3,-2,2,2,2,-2,3,
%U A157986 2,-2,2,2,-11,2,-7,-3,-2,2,-4,2,2,2,3,-2,2,2,-5,2,2,2,3,-2,2,-2,2,2,-12,2,2
%N A157986 Largest exponents of perfect powers (m^k where m is an integer and k >= 2) multiplied by -1 when base m is prime (m^k thus a prime power).
%H A157986 Daniel Forgues, <a href="/A157986/b157986.txt">Table of n, a(n) for n=1..10000</a>
%F A157986 a(n) = {k}_n * (-1)^(Pi(m) - Pi(m-1)) where {k}_n is the exponent of {m^k}_n (the n-th perfect power with positive integer base m corresponding to largest integer exponent k) and Pi(m) is the prime counting function evaluated at m.
%F A157986 a(n) = A025479(n) * (-1)^{Pi(m) - Pi(m-1)}, with m = A001597(n)^(1/(A025479(n))).
%Y A157986 Cf. A001597 (perfect powers), A025479 (largest exponents of perfect powers).
%Y A157986 Cf. A025478 (least roots of perfect powers).
%Y A157986 Cf. A157985.
%K A157986 sign
%O A157986 1,1
%A A157986 _Daniel Forgues_, Mar 10 2009