COUNTING SUBGROUPS OF Z/paZ× Z/pbZ
نویسنده
چکیده
Fix a prime p. For nonnegative integers a, b, and d, we seek a formula for the number of subgroups of order pd in Z/paZ× Z/pbZ. Set Na,b,d = #{H ⊂ Z/pZ× Z/pZ : #H = p}. This is symmetric in a and b (Na,b,d = Nb,a,d), so when it is convenient we can limit attention to the case a ≤ b. Trivially Na,b,d = 0 if d > a + b, so we may assume 0 ≤ d ≤ a + b. For 1 ≤ a ≤ b, and a + b ≥ d, we will see that Na,b,d = 1 + p + p 2 + · · ·+ p,
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