the first letter is 1 to the right, then the second is 2 from the frst, then the third is 4 from the second, then the fourth is 6 from the third, then the fifth is 7 from the fourth, therefore the the sixth should be 9 from the fifth or the letter h. so the pattern is 1, n+1, n+3, n+5, n+6, n +7, n+9.