A096549 Least exponent k such that the lowest n digits in the decimal representation of 2^k are even.

1, 6, 10, 11, 19, 43, 50, 50, 71, 71, 523, 590, 590, 12106, 12106, 12106, 12106, 56590, 505206, 1570511, 1570511, 4033966, 4033966, 9525771, 24045606, 24045606, 57862019, 183002599, 183002599, 877875719, 877875719, 877875719, 3789535319

Offset: 1

Author

Hugo Pfoertner, Jul 07 2004

Keywords

• base
• nonn

Comments

This problem was discussed in a thread "Power of 2 with all even digits?" in the newsgroup sci.math (Jun 25 2004) with contributions from Edwin Clark, James Waldby, Bertram Felgenhauer, Richard Tobin, Oskar Lanzi III and others.

a(47) > 15258789062500. - Robert Xiao, Mar 23 2025

Examples

			a(5)=19 because 2^19=524288 is the smallest power of 2 that has a decimal representation ending in 5 even digits.
		

Links

• Robert Xiao, Table of n, a(n) for n = 1..46
• Newsgroup sci.math, Power of 2 with all even digits?

Crossrefs

Cf. A000079, A068994.

Extensions

a(21)-a(33) from Richard Tobin (richard(AT)cogsci.ed.ac.uk), Jun 29 2004