|
%I #9 Feb 06 2022 10:07:07
%S 1,2,5,12,30,81,224,626,1747,4909,13811,38934,109889,310666,880125,
%T 2500221,7125406,20376598,58472481,168349612,486198698
%N a(n) = 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. A261786, A000244, A261396, A261806.
%K nonn,more
%O 0,2
%A _Reinhard Zumkeller_, Sep 01 2015
%E a(11)-a(20) from _Michel Marcus_, Feb 06 2022
|
