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%I #7 Jun 25 2022 00:33:47
%S 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,
%T 10,10,10,11,11,11,11,11,11,12,12,12,12,12,12,13,13,14,14,14,14,14,14,
%U 14,14,14,14,14,14,15,15,15,15,16,16,17,17,17,17,18,18,19,19,19,19,20,20
%N Number of lucky numbers <= n.
%D R. K. Guy, Unsolved Problems in Number Theory, C3.
%H V. Gardiner, R. Lazarus, N. Metropolis, and S. Ulam, <a href="https://www.jstor.org/stable/3029719">On certain sequences of integers defined by sieves</a>, Mathematics Magazine, 29(3) (1955), 117-122.
%H Martin Gardner, <a href="http://dx.doi.org/10.1007/BF03024427">Lucky numbers and 2187</a>, Math. Intellig., 19(2) (1997), 26-29.
%H I. Peterson, MathTrek, <a href="http://www.sciencenews.org/pages/sn_arc97/9_6_97/mathland.htm">Martin Gardner's Lucky Numbers</a>
%H Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/LuckyNumber.html">Lucky Number</a>
%H Wikipedia, <a href="http://en.wikipedia.org/wiki/Lucky_number">Lucky Number</a>
%e a(9)=4 because there are 4 lucky numbers less than or equal to 9 (1, 3, 7, 9)
%Y Cf. A000959.
%Y Partial sums of A145649.
%K nonn
%O 0,3
%A Shawn M. Moore (sartak(AT)gmail.com), Jun 30 2005
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