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

0, 2, 18, 44, 192, 315, 3396, 8556, 13327, 81785, 279267, 865357, 1799674, 1727603, 8760851, 63416791, 106892452

Offset

0,2

Links

Table of n, a(n) for n=0..16.

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,changed

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

a(16) from Paul Geneau de Lamarlière, Jun 26 2024

a(0)=0 prepended by Paul Geneau de Lamarlière, Jul 20 2024

Status

approved