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A362316
Expansion of e.g.f (exp(x)-1)*(exp(2*x)-1).
1
0, 0, 4, 18, 64, 210, 664, 2058, 6304, 19170, 58024, 175098, 527344, 1586130, 4766584, 14316138, 42981184, 129009090, 387158344, 1161737178, 3485735824, 10458256050, 31376865304, 94134790218, 282412759264, 847255055010, 2541798719464, 7625463267258, 22876524019504, 68629840493970
OFFSET
0,3
COMMENTS
Number of ternary strings with at least one 0 or one 1 and at least one 2.
FORMULA
a(n) = 3^n - 2^n - 1, n>0; a(0)=0.
a(n) = 2*A053152(n).
EXAMPLE
The 4 strings for n=4 are 12, 21, 02, 20.
MATHEMATICA
LinearRecurrence[{6, -11, 6}, {0, 0, 4, 18}, 30] (* Paolo Xausa, Aug 07 2023 *)
CROSSREFS
Cf. A001550, A053152, A083321 (alternates signs).
Sequence in context: A212766 A100177 A083321 * A255611 A022728 A231950
KEYWORD
nonn,easy
AUTHOR
Enrique Navarrete, Apr 16 2023
STATUS
approved