• 0.56714 32904 09783..., the Omega constant (Ω). The Omega constant is defined by the equation,

• 0.57721 56649 01532..., the Euler–Mascheroni constant (γ), is the limit of the difference between the harmonic series and the natural logarithm, so it's related to the Meissel–Mertens constant. It's larger, since the harmonic series sums the reciprocals of all positive integers, and not just the prime numbers.

• 0.66016 18158 46869..., the Twin prime constant (C

[p(p-2)]/[(p-1)^{2}]

• 0.87058 83800 (approximately), Brun's constant (B

0.12345 67891 01112 13141 51617...,is built in such a way. If you haven't yet guessed it, this constant is formed by placing a decimal point in front of the positive integers. The individual decimal digits forming the Champernowne constant are sequence A033307 in the OEIS. Likewise, there's a Champernowne constant in base-2,

0.11011 10010 11101...The Thue-Morse sequence (OEIS A010060) is especially understandable to computer scientists, since it involves the two's complement of numbers. Two ways in which this constant can be defined are as follow:

1) Start with a string that's just the single characterNot surprisingly, there's a lot of symmetry in such a number when it's viewed in chunks that are powers of two in length, as shown in the following figure. This figure was generated from a file created by my own program for generating the Thue-Morse sequence. The source code for the program can be found here. Thue-Morse Constant with value0, and repeatedly apply the replacement rules0 -> 01and1 -> 10to the characters of the string.

2) Start with a string that's just the single character0, and repeatedly append the binary complement of the string to itself; that is, repeatedly concatenate copies of the string in which all ones have become zeros, and all zeros have become ones.

0.01101 00110 01011... (base-2)The Thue-Morse sequence might not be mathematically important, but it illustrates how a very simple rule can generate some interesting results. Another example is the logistic map.

0.41245 40336 40107... (base-10)

- The US House of Representatives, in its 2009-2010 session (the 111th Congress), passed a resolution supporting March 14 as Pi Day on March 12, 2009. The text of the resolution contains the following:
"...Whereas Pi can be approximated as 3.14, and thus March 14, 2009, is an appropriate day for ''National Pi Day'': Now, therefore, be it Resolved, That the House of Representatives-(1) supports the designation of a ''Pi Day'' and its celebration around the world..."

The full text of the resolution (H.Res. 224) can be found here.

- Eric W. Weisstein, "Thue-Morse Constant," From MathWorld--A Wolfram Web Resource