A242594 Numbers k such that 4^k has initial digit 4.

1, 6, 11, 16, 21, 26, 31, 36, 41, 46, 99, 104, 109, 114, 119, 124, 129, 134, 139, 144, 197, 202, 207, 212, 217, 222, 227, 232, 237, 242, 295, 300, 305, 310, 315, 320, 325, 330, 335, 393, 398, 403, 408, 413, 418, 423, 428, 433, 491, 496, 501, 506, 511, 516, 521, 526, 531, 584, 589, 594, 599, 604, 609, 614, 619

Offset: 1

Author

Robert Israel, May 18 2014

Keywords

• nonn
• base

Examples

			6 is in the sequence because 4^6 = 4096 starts with 4.
		

Links

• Robert Israel, Table of n, a(n) for n = 1..9693

Crossrefs

Cf. A067482.

Programs

Maple

select(t -> 4^t >= 4*10^ilog10(4^t) and 4^t < 5*10^ilog10(4^t), [$1..1000]); # Robert Israel, May 18 2014

Formula

a(n) = log_4(A067482(n)).