a(n)=16^n - 3*2^(2*n - 1) - 1.

A152101

a(n)=16^n - 3*2^(2*n - 1) - 1.

Terms

    a(0) =9a(1) =231a(2) =3999a(3) =65151a(4) =1047039a(5) =16771071a(6) =268410879a(7) =4294868991a(8) =68719083519

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