Across: A: a prime number
D: A down / C down
F: a prime number
G: a square number
H: add two to E down and multiply the result with the sum of the digits of D across to get H across.
Down: A: see D across.
B: the reverse of A across
C: The sum of C down's digits equals the first digit of D across.
E: A palindrome (a number that is equal to its reverse).