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A359962 Number of multisets of n nonempty words with a total of 2n letters over binary alphabet. 3
1, 4, 26, 132, 623, 2632, 10500, 39384, 141659, 490100, 1644186, 5366436, 17113433, 53454528, 163963312, 494786352, 1471423866, 4318092136, 12520027756, 35901819336, 101909674398, 286575107424, 798886300056, 2209115439664, 6062818714752, 16522049256656 (list; graph; refs; listen; history; text; internal format)
OFFSET
0,2
LINKS
FORMULA
a(n) = [x^(2*n)*y^n] Product_{j>=1} 1/(1-y*x^j)^(2^j).
a(n) = A209406(2n,n).
EXAMPLE
a(0) = 1: {}.
a(1) = 4: {aa}, {ab}, {ba}, {bb}.
a(2) = 26: {a,aaa}, {a,aab}, {a,aba}, {a,abb}, {a,baa}, {a,bab}, {a,bba}, {a,bbb}, {aa,aa}, {aa,ab}, {aa,ba}, {aa,bb}, {aaa,b}, {aab,b}, {ab,ab}, {ab,ba}, {ab,bb}, {aba,b}, {abb,b}, {b,baa}, {b,bab}, {b,bba}, {b,bbb}, {ba,ba}, {ba,bb}, {bb,bb}.
CROSSREFS
Sequence in context: A184263 A058408 A053906 * A316539 A197964 A100236
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Jan 20 2023
STATUS
approved

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Last modified February 23 17:43 EST 2024. Contains 370283 sequences. (Running on oeis4.)