Terms in a multinomial expansion

MediumCombinatorics~4m

After combining like terms, how many distinct terms appear in the expansion of (x1+x2+x3+x4+x5+x6)18(x_1 + x_2 + x_3 + x_4 + x_5 + x_6)^{18}?

Show hints (2)+
  1. A term is an exponent tuple (e1,,e6)(e_1,\dots,e_6) with ei=18\sum e_i = 18, ei0e_i\ge0.
  2. Stars and bars: (18+55)=(235)\binom{18+5}{5}=\binom{23}{5}.

Answer

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