No simple groups of order 4851 or 5145 exist

Prove that there are no simple groups of order 4851 or 5145.


  1. Note that 4851 = 3^2 \cdot 7^2 \cdot 11. Suppose G is a simple group of order 4851. By Sylow’s Theorem, we have n_3(G) \in \{7,49\} and n_{11}(G) = 441. Note that |G| does not divide 10!, so that no subgroup of G has index less than or equal to 10. In particular, n_3(G) = [G:N_G(P_3)] \neq 7, so that n_3(G) = 49. Let P_3 \in \mathsf{Syl}_3(G). We have |N_G(P_3)| = 3^2 \cdot 11. By Cauchy, there exists a Sylow 11-subgroup P_{11} \leq N_G(P_3). Now P_3P_{11} \leq G is a subgroup, and since 3 does not divide 10 and 11 does not divide 8, by this previous exercise, P_3P_{11} is abelian. Thus we have P_3 \leq N_G(P_{11}). But we also know that |N_G(P_{11})| = 11, a contradiction.
  2. Note that 5145 = 3 \cdot 5 \cdot 7^3. Suppose G is a simple group of order 5145. Note that |G| does not divide 20! since the largest power of 7 dividing 20! is 7^2. Thus G has no proper subgroups of index less than or equal to 20. In particular, from Sylow’s Theorem we have n_7(G) = 1, a contradiction.
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