To find the value of a1, we need to use the formula for an arithmetic sequence:

an = a1 + (n-1)d

Where:
an = the value of the nth term
a1 = the first term
d = the common difference between terms
n = the term number

Given that S25 = 100 and a25 = -44, we can calculate the sum of the first 25 terms of the sequence using the formula for the sum of an arithmetic series:

Sn = (n/2)(a1 + an)

100 = (25/2)(a1 + (-44))
100 = (12.5)(a1 - 44)
100 = 12.5a1 - 550
650 = 12.5a1
a1 = 52

Therefore, the value of a1 is 52.