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a(n) = floor(n * log(4/3) / log(3/2))
1

%I #70 Jan 29 2024 19:26:07

%S 0,0,1,2,2,3,4,4,5,6,7,7,8,9,9,10,11,12,12,13,14,14,15,16,17,17,18,19,

%T 19,20,21,21,22,23,24,24,25,26,26,27,28,29,29,30,31,31,32,33,34,34,35,

%U 36,36,37,38,39,39,40,41,41,42,43,43,44,45,46,46,47,48

%N a(n) = floor(n * log(4/3) / log(3/2))

%C Highest k with 3^(n+k) <= 4^n * 2^k.

%F a(n) = floor(n * log(3) / log(3/2)) - 2*n.

%F a(n) = floor(n * arctanh(1/7) / arctanh(1/5)).

%F a(n) = A325913(n) - n.

%F a(n) = A117630(n) - 2*n.

%F a(n) = A054414(n) - 2*n - 1.

%t Table[Floor[n*Log[4/3]/Log[3/2]],{n,0,68}] (* _James C. McMahon_, Jan 27 2024 *)

%o (PARI) alist(N) = my(a=-1, b=1, k=0); vector(N, i, a+=2; b*=3; if(logint(b, 2) < a, a++; b*=3; k++); k); \\ note that i is n+1

%Y Cf. A054414, A117630, A325913, A369522 (slope).

%K nonn,easy

%O 0,4

%A _Ruud H.G. van Tol_, Jan 25 2024