cp's OEIS Frontend

A131551 Least power of 3 having exactly n consecutive 2's in its decimal representation.

%I A131551 #13 Mar 19 2021 10:22:05
%S A131551 3,19,148,253,330,2380,2124,30598,22791,238582,107187,1521134,
%T A131551 10363119,9995030,68353787
%N A131551 Least power of 3 having exactly n consecutive 2's in its decimal representation.
%e A131551 a(3)=148 because 3^148 (i.e. 41109831670569663658300086939077404909608122265524774868353822811305361) is the smallest power of 3 to contain a run of 3 consecutive twos in its decimal form.
%t A131551 a = ""; Do[ a = StringJoin[a, "2"]; b = StringJoin[a, "2"]; k = 1; While[ StringPosition[ ToString[3^k], a] == {} || StringPosition[ ToString[3^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
%o A131551 (Python)
%o A131551 def a(n):
%o A131551   k, n2, np2 = 1, '2'*n, '2'*(n+1)
%o A131551   while True:
%o A131551     while not n2 in str(3**k): k += 1
%o A131551     if np2 not in str(3**k): return k
%o A131551     k += 1
%o A131551 print([a(n) for n in range(1, 8)]) # _Michael S. Branicky_, Mar 19 2021
%Y A131551 Cf. A195269, A131552, A131550, A131549, A131548, A131547, A131546, A131545, A131544.
%K A131551 more,nonn,base
%O A131551 1,1
%A A131551 _Shyam Sunder Gupta_, Aug 26 2007
%E A131551 a(11)-a(14) from _Lars Blomberg_, Feb 02 2013
%E A131551 a(15) from _Bert Dobbelaere_, Mar 04 2019