A109497 Number of lucky numbers <= n.

1, 1, 2, 2, 2, 2, 3, 3, 4, 4, 4, 4, 5, 5, 6, 6, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 8, 9, 9, 10, 10, 10, 10, 11, 11, 11, 11, 11, 11, 12, 12, 12, 12, 12, 12, 13, 13, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 17, 17, 17, 17, 18, 18, 19, 19, 19, 19, 20, 20

Offset: 0

Author

Shawn M. Moore (sartak(AT)gmail.com), Jun 30 2005

Keywords

• nonn

Examples

			a(9)=4 because there are 4 lucky numbers less than or equal to 9 (1, 3, 7, 9)
		

References

• R. K. Guy, Unsolved Problems in Number Theory, C3.

Links

• V. Gardiner, R. Lazarus, N. Metropolis, and S. Ulam, On certain sequences of integers defined by sieves, Mathematics Magazine, 29(3) (1955), 117-122.
• Martin Gardner, Lucky numbers and 2187, Math. Intellig., 19(2) (1997), 26-29.
• I. Peterson, MathTrek, Martin Gardner's Lucky Numbers
• Eric Weisstein's World of Mathematics, Lucky Number
• Wikipedia, Lucky Number

Crossrefs

Cf. A000959.

Partial sums of A145649.