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 A342912 a(n) = [x^n] (1 - 2*x - sqrt((1 - 3*x)/(1 + x)))/(2*x^3). 1
 1, 1, 3, 6, 15, 36, 91, 232, 603, 1585, 4213, 11298, 30537, 83097, 227475, 625992, 1730787, 4805595, 13393689, 37458330, 105089229, 295673994, 834086421, 2358641376, 6684761125, 18985057351, 54022715451, 154000562758, 439742222071, 1257643249140, 3602118427251 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 LINKS FORMULA a(n) = (2*a(n - 1) + 3*a(n - 2))*(n + 1)/(n + 3) for n >= 3. a(n) = (-1)^n*hypergeom([1/2, -2 - n], [2], 4]. a(n) ~ (3^(n + 7/2)*(16*n + 11))/(128*sqrt(Pi)*(n + 2)^(5/2)). MAPLE gf := (1 - 2*x - sqrt((1 - 3*x)/(1 + x)))/(2*x^3): ser := series(gf, x, 36): seq(coeff(ser, x, n), n = 0..30); a := proc(n) option remember; `if`(n < 3, [1, 1, 3][n + 1], ((2*a(n - 1) + 3*a(n - 2))*(n + 1))/(n + 3)) end: seq(a(n), n=0..30); MATHEMATICA a[n_] := (-1)^n*HypergeometricPFQ[{1/2, -2 - n}, {2}, 4] Table[a[n], {n, 0, 30}] PROG (Python) def rnum():     a, b, n = 1, 3, 3     yield 1     yield 1     while True:         yield b         n += 1         a, b = b, (n*(3*a + 2*b))//(n + 2) A342912 = rnum() print([next(A342912) for _ in range(31)]) CROSSREFS The diagonal sums of the Motzkin triangle A064189 (with the Motzkin numbers A001006 as first column), the row sums of A020474, and a shifted version of the Riordan numbers A005043. Sequence in context: A174297 A005043 A099323 * A058534 A063778 A279374 Adjacent sequences:  A342909 A342910 A342911 * A342913 A342914 A342915 KEYWORD nonn AUTHOR Peter Luschny, Apr 18 2021 STATUS approved

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Last modified June 22 13:46 EDT 2021. Contains 345380 sequences. (Running on oeis4.)