OFFSET

1,1

COMMENTS

a(15) > 10^8, a(16)=82011442, a(17)=78927180. - Bert Dobbelaere, Mar 20 2019

EXAMPLE

a(3)=55 because 3^55 (i.e., 174449211009120179071170507) is the smallest power of 3 to contain a run of 3 consecutive fours in its decimal form.

MATHEMATICA

a = ""; Do[ a = StringJoin[a, "4"]; b = StringJoin[a, "4"]; k = 1; While[ StringPosition[ ToString[3^k], a] == {} || StringPosition[ ToString[3^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]

PROG

(Python)

def a(n):

target, antitarget = '4'*n, '4'*(n+1)

k, pow3 = 1, 3

while True:

t = str(pow3)

if target in t and antitarget not in t: return k

k, pow3 = k+1, pow3*3

print([a(n) for n in range(1, 9)]) # Michael S. Branicky, May 12 2021

CROSSREFS

KEYWORD

more,nonn,base

AUTHOR

Shyam Sunder Gupta, Aug 26 2007

EXTENSIONS

a(11)-a(14) from Lars Blomberg, Feb 02 2013

STATUS

approved