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 A162459 #9 Mar 31 2021 10:11:04 %S A162459 1,0,-4,-8,-32,-32,-128,-256,-512,-512,-2048,-4096,-12288,-16384, %T A162459 -16384,-32768,-131072,-262144,-786432,-1572864,-2097152,-2097152, %U A162459 -8388608,-16777216,-33554432,-33554432,-67108864,-134217728,-536870912,-1610612736,-4294967296 %N A162459 A002321*A000079. %C A162459 Appears to be the determinant of n X n (-1,1) matrix defined by A(i,j)=1 if j=1 or i divides j else -1. %C A162459 Appears also to be the determinant of n X n (-i/j,i/j) matrix defined by A(i,j)=i/j if j=1 or i divides j else -i/j. %F A162459 a(n) = 2^(n-1)*A002321(n). - _Chai Wah Wu_, Mar 30 2021 %o A162459 (Python) %o A162459 from functools import lru_cache %o A162459 @lru_cache(maxsize=None) %o A162459 def A162459(n): %o A162459 if n == 0: %o A162459 return 0 %o A162459 c, j = n, 2 %o A162459 k1 = n//j %o A162459 while k1 > 1: %o A162459 j2 = n//k1 + 1 %o A162459 c += (j2-j)*A162459(k1)//2**(k1-1) %o A162459 j, k1 = j2, n//j2 %o A162459 return 2**(n-1)*(j-c) # _Chai Wah Wu_, Mar 30 2021 %Y A162459 Cf. A002321, A000079. %K A162459 sign %O A162459 1,3 %A A162459 _Mats Granvik_, Jul 04 2009