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 A128251 #8 Feb 16 2025 08:33:04 %S A128251 15,5,255,39,1295,150,4095,410,9999,915,20735,1785,38415,3164,65535, %T A128251 5220,104975,8145,159999,12155,234255,17490,331775,24414,456975,33215, %U A128251 614655,44205,809999,57720,1048575,74120,1336335,93789,1679615,117135 %N A128251 n^4 - 1 divided by its largest fourth power divisor. %C A128251 In other words, biquadratefree part of n^4-1, or biquadratefree kernel of n^4-1. Fourth power analog of what A128972 is to cubes and A068310 is to squares. A046100 Biquadratefree numbers. A008835 Largest 4th power dividing n. %H A128251 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/Biquadratefree.html">Biquadratefree.</a> %F A128251 a(n) = (n^4 - 1)/A008835(n^4 - 1) = (A000583(n)-1)/A008835((A000583(n)-1)). %e A128251 a(3) = 5 because (3^4 - 1)/16 = 80/16 = (2^4 * 5)/(2^4) = 5. %e A128251 a(5) = 39 because (5^4 - 1)/16 = 624/16 = (2^4 * 3 * 13)/(2^4) = 39. %e A128251 a(7) = 150 because (7^4 - 1)/16 = 2400/16 = (2^5 * 3 * 5^2)/(2^4) = 150. %e A128251 a(9) = 410 because (9^4 - 1)/16 = 6560/16 = (2^5 * 5 * 41)/(2^4) = 410. %e A128251 a(63) = 61535 because (63^4 - 1)/256 = 15752960/256 = (2^8 * 5 * 31 * 397)/(2^8) = 61535. %Y A128251 Cf. A000188, A000583, A002350, A004709, A007948, A008835, A062378, A067872, A033314, A068310, A128972. %K A128251 easy,nonn %O A128251 2,1 %A A128251 _Jonathan Vos Post_, May 03 2007