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 A386221 #41 Aug 27 2025 22:04:06 %S A386221 2371610879733375,8379443074856875,103889625367330285, %T A386221 162508095102648823,2143169709271976875,2481725627762299375, %U A386221 4055619414785589625,8167773178498814075,9027536760163222895,133527604616779133915,133893081609954481115,137216105281788994475,457495296809227508125 %N A386221 Numbers which can be expressed as the product of a number and its binary reversal in at least three different ways. %C A386221 It appears that most numbers that can be expressed in three different ways can also be expressed in four different ways. For a(n) < 2^88, only 11 numbers can be expressed in exactly three ways while 691 numbers can be expressed in exactly four ways. %H A386221 Shou'en Wang, <a href="https://bbs.emath.ac.cn/forum.php?mod=viewthread&tid=19957">Binary reversal</a> (Chinese) %e A386221 2371610879733375 = 51606261*45955875 = 64244529*36915375 = 64338225*36861615 while 51606261 = 11000100110111001011110101_2, 45955875 = 10101111010011101100100011_2 and reverse(11000100110111001011110101) = 10101111010011101100100011. %e A386221 8379443074856875 = 101377465*82655875 = 102886105*81443875 = 114021425*73490075 = 115718225*72412475. %Y A386221 Cf. A066531, A066598. %K A386221 nonn,base,new %O A386221 1,1 %A A386221 _Zhao Hui Du_, Aug 12 2025