 The function formula_1 is defined for all even integers formula_3 to be the number of different ways in which "E" can be expressed as the sum of two primes.For example, formula_4 since 22 can be expressed as the sum of two primes in three different ways (formula_5).The coloring of points in the above image is based on the value of formula_6 modulo 3 with red points corresponding to 0 mod 3, blue points corresponding to 1 mod 3 and green points corresponding to 2 mod 3.