the first two months of leap years.

For example, to find the Dominical Letter of the year 1913:

*1900 is G and 13 corresponds to 5
*G + 5 = G - 2 = E, so 1913 is E
*Sundays of 1913 were on E days (e.g. January 5)

Similarly, for 2007:
*2000 is BA and 7 corresponds to 6
*A + 6 = A - 1 = G, so 2007 is G
*Sundays of 2007 were on G days (e.g. January 7)

For leap year 2040:
*2000 is BA and 40 mod 28 = 12
*For the first two months of 2040, red 12 corresponds