A131538 Least power of 2 having exactly n consecutive 4's in its decimal representation.

2, 18, 44, 192, 315, 3396, 8556, 13327, 81785, 279267, 865357, 1799674, 1727603, 8760851, 63416791

Offset

1,1

Comments

No more terms < 28*10^6.

Links

Table of n, a(n) for n=1..15.

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

Example

a(3)=44 because 2^44(i.e. 17592186044416) is the smallest power of 2 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[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]

Crossrefs

Sequence in context: A296266 A365493 A280316 * A009820 A304933 A126909

Adjacent sequences: A131535 A131536 A131537 * A131539 A131540 A131541

Keyword

more,nonn,base

Author

Shyam Sunder Gupta, Aug 26 2007

Extensions

3 more terms from Sean A. Irvine, Jul 19 2010

a(14) from Lars Blomberg, Jan 24 2013

a(15) from Bert Dobbelaere, Feb 25 2019

Status

approved