A259089 Least k such that 2^k has at least n consecutive 2's in its decimal representation.

0, 1, 43, 43, 314, 314, 2354, 8555, 13326, 81784, 279272, 865356, 1727602, 1727602

Offset

0,3

Links

Table of n, a(n) for n=0..13.

Popular Computing (Calabasas, CA), Two Tables, Vol. 1, (No. 9, Dec 1973), page PC9-16.

Example

a(3)=43 because 2^43 (i.e. 8796093022208) is the smallest power of 2 to contain a run of 3 consecutive twos in its decimal form.

Mathematica

Table[k = 0; While[! SequenceCount[IntegerDigits[2^k], ConstantArray[2, n]] > 0, k++]; k, {n, 10}] (* Robert Price, May 17 2019 *)

Prog

(Python)
def A259089(n):
....s, k, k2 = '2'*n, 0, 1
....while True:
........if s in str(k2):
............return k
........k += 1
........k2 *= 2 # Chai Wah Wu, Jun 19 2015

Crossrefs

Cf. A006889, A131535, A131536, A063565, A259091, A259092.

Sequence in context: A291494 A051614 A291479 * A165864 A223746 A020442

Adjacent sequences: A259086 A259087 A259088 * A259090 A259091 A259092

Keyword

more,nonn,base

Author

N. J. A. Sloane, Jun 18 2015

Extensions

a(7)-a(13) from Chai Wah Wu, Jun 20 2015

Definition corrected by Manfred Scheucher, Jun 23 2015

a(0) prepended by Chai Wah Wu, Jan 28 2020

Status

approved