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 A216761 #15 Dec 06 2019 21:44:02
%S A216761 1,2,3,8,10,12,14,24,27,30,33,36,39,42,45,128,136,144,152,160,168,176,
%T A216761 184,192,200,208,216,224,232,240,248,320,330,340,350,360,370,380,390,
%U A216761 400,410,420,430,440,450,460,470,480,490,500,510,520,530,540,550
%N A216761 n * floor(log_2(n)) * floor(log_2(log_2(n))) * floor(log_2(log_2(log_2(n)))) ....
%C A216761 a(n) is the product of n, floor(log_2 n), floor (log_2(log_2 n)), ... with the base-2 logs iterated while the result remains greater than unity.
%C A216761 The sum of the reciprocals of a(n) diverge, but extremely slowly.
%C A216761 In particular, the sum of the reciprocals acts like lg* n asymptotically, where lg* x = 0 for x < 2 and lg* 2^x = 1 + lg* x. - _Charles R Greathouse IV_, Sep 25 2012
%e A216761 a(0) is the product of 0 numbers, defined to be 1.
%e A216761 a(15) = 15 * floor(log_2 15) * floor(log_2 log_2 15) = 15 * 3 * 1 = 45.
%e A216761 a(17) = 17 * floor(log_2 17) * floor(log_2 log_2 17) * floor(log_2 log_2 log_2 17) = 17 * 4 * 2 * 1 = 136.
%t A216761 Table[prod = 1; s = n; While[s > 1, prod = prod*Floor[s]; s = Log[2, s]]; prod, {n, 60}] (* _T. D. Noe_, Sep 24 2012 *)
%o A216761 (Haskell) a = product . map floor . takeWhile (1<) . iterate log_2
%o A216761 (PARI) a(n)=my(t=n);n+=1e-9;while(n>2,t*=floor(n=log(n)/log(2)));t \\ _Charles R Greathouse IV_, Sep 25 2012
%Y A216761 Cf. A216762 (ceiling instead of floor).
%K A216761 nonn
%O A216761 1,2
%A A216761 _Ken Takusagawa_, Sep 15 2012