A261788 a(n) is the smallest k such that A261786(k) >= 3^n.

1, 2, 5, 12, 30, 81, 224, 626, 1747, 4909, 13811, 38934, 109889, 310666, 880125, 2500221, 7125406, 20376598, 58472481, 168349612, 486198698, 1408140693, 4088769215, 11899761717, 34703682407

Offset: 0

Author

Reinhard Zumkeller, Sep 01 2015

Keywords

• nonn
• more

Crossrefs

Cf. A000244, A261396, A261786, A261806.

Programs

Haskell

a261788 n = a261788_list !! (n-1)
a261788_list = f 1 1 a261786_list' where
   f z k (x:xs) | x >= z    = k : f (3 * z) (k + 1) xs
                | otherwise = f z (k + 1) xs

PARI

ts(n) = Str(fromdigits(digits(n, 3))); \\ A007089
f(n) = my(s=ts(n), k=1); while (#strsplit(s, ts(k)) != 1, k++); k; \\ A261787
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

Extensions

a(11)-a(20) from Michel Marcus, Feb 06 2022

a(21)-a(24) from Jinyuan Wang, Dec 13 2024