A261788 - OEIS

%I #13 Dec 14 2024 05:30:39

%S 1,2,5,12,30,81,224,626,1747,4909,13811,38934,109889,310666,880125,

%T 2500221,7125406,20376598,58472481,168349612,486198698,1408140693,

%U 4088769215,11899761717,34703682407

%N a(n) is the smallest k such that A261786(k) >= 3^n.

%o (Haskell)

%o a261788 n = a261788_list !! (n-1)

%o a261788_list = f 1 1 a261786_list' where

%o    f z k (x:xs) | x >= z    = k : f (3 * z) (k + 1) xs

%o                 | otherwise = f z (k + 1) xs

%o (PARI) ts(n) = Str(fromdigits(digits(n, 3))); \\ A007089

%o f(n) = my(s=ts(n), k=1); while (#strsplit(s, ts(k)) != 1, k++); k; \\ A261787

%o lista(nn) = my(last=1, k=0, p=3^k); for (n=1, nn, if (last >= p, print1(n, ", "); k++; p = 3^k); last += f(last);); \\ _Michel Marcus_, Feb 06 2022

%Y Cf. A000244, A261396, A261786, A261806.

%K nonn,more

%O 0,2

%A _Reinhard Zumkeller_, Sep 01 2015

%E a(11)-a(20) from _Michel Marcus_, Feb 06 2022

%E a(21)-a(24) from _Jinyuan Wang_, Dec 13 2024