# How to interpret a formula from the handbook of applied cryptography

In the handbook of applied cryptography, we can find the following formula for testing PRNG. My question is what does mean 2 in the upper index of the n_00 and others? It is not power because then the formula does not make sense.

• $n_{ab}$ should be the number of the sequence ab appearing, so squaring over the integer should make sense here? – SEJPM Mar 6 '18 at 19:40
• As you can see it follow chi square so result shall be bellow 1.0 – whd Mar 6 '18 at 21:20
• Did you mean this "answer" to be a response to my comment or to kodlu's (community wiki) answer? – SEJPM Mar 6 '18 at 21:22
• This does not provide an answer to the question. Once you have sufficient reputation you will be able to comment on any post; instead, provide answers that don't require clarification from the asker. - From Review – Maeher Mar 7 '18 at 4:21
• whd, you may want to merge your two accounts. – SEJPM Mar 7 '18 at 12:45

The comment by @SEJPM is correct, all those subscripted $n_0,n_{01}$ etc are nonnegative integers counting the occurrences of subsequences such as $0,01$ respectively.