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 A065761 #13 Oct 16 2023 12:03:44
%S A065761 0,3,24,399,12768,817215,104603520,26778501375,13710592704000,
%T A065761 14039646928897023,28753196910381103104,117773094544920998318079,
%U A065761 964797190511992818221703168,15807237169348490333744384720895
%N A065761 Concatenation of increasing number of alternating digits in base 2, starting with 0.
%C A065761 The first 5 terms in base 2 are 0, (0)11, (0)11000, (0)110001111, (0)11000111100000.
%H A065761 Harry J. Smith, <a href="/A065761/b065761.txt">Table of n, a(n) for n = 1..50</a>
%F A065761 a(1) = 0; a(n+1) = append n+1 0's or 1's (alternately) to a(n).
%e A065761 a(5) = 12768 is formed by appending 0 five times (00000) to a(4) in base 2: (0)11000111100000.
%o A065761 (PARI) baseI(x, b)= { local(d, e=0, f=1); while (x>0, d=x-10*(x\10); x\=10; e+=d*f; f*=b); return(e) } { c=1; for (n=1, 50, if (n==1, a=0; b=0, c=c*10 + 1; if (n%2, d=0, d=c); b=b*10^n + d; a=baseI(b, 2)); write("b065761.txt", n, " ",a) ) } \\ _Harry J. Smith_, Oct 30 2009
%Y A065761 Cf. A065760, A065447.
%K A065761 base,easy,nonn
%O A065761 1,2
%A A065761 _Lior Manor_, Nov 18 2001