n This appears to be the initial letters of (most of) the first nine numbers, spelled out: o = one; t = two; t = three; f = four or five; s = six; s = seven; e = eight; n = nine
the next letter should be 't' (for 'ten'), although the missing 'f' could be intentionally part of a pattern. If 'five' was left out, then 'ten' should be left out as well; the next letter in that case would be 'e', for 'eleven'.
Theta for the sound of th in "thin;" delta for the sound of th in "this."
In 2016
a letter
toern
linseed
9739527531 th march
eggs
trivia
1st, 2nd, 3rd, 4th, 5th, 6th.... Ans: th
theta
Th next higher command has DMETL approval.
Th next higher command has DMETL approval.