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 A027262 a(n) = self-convolution of row n of array T given by A026519. 21
 1, 3, 8, 58, 196, 1608, 5774, 48924, 180772, 1553940, 5837908, 50618184, 192239854, 1676640462, 6416509142, 56201554888, 216309089956, 1900789437276, 7347943049432, 64734185205960, 251119894730596, 2216888144737508, 8624336421678788, 76265067399850848, 297394187356638766 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 LINKS G. C. Greubel, Table of n, a(n) for n = 0..1000 FORMULA a(n) = Sum_{k=0..2*n} A026519(n, k)*A026519(n, 2*n-k). MATHEMATICA T[n_, k_]:= T[n, k]= If[k<0 || k>2*n, 0, If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[(n+1)/2], If[EvenQ[n], T[n-1, k-2] + T[n-1, k], T[n-1, k-1] + T[n-1, k-2] + T[n-1, k] ]]]]; (* T = A026519 *) a[n_]:= a[n]= Block[{\$RecursionLimit = Infinity}, Sum[T[n, k]*T[n, 2*n-k], {k, 0, 2*n}] ]; Table[a[n], {n, 0, 40}] (* G. C. Greubel, Dec 21 2021 *) PROG (Sage) @CachedFunction def T(n, k): # T = A026519     if (k<0 or k>2*n): return 0     elif (k==0 or k==2*n): return 1     elif (k==1 or k==2*n-1): return (n+1)//2     elif (n%2==0): return T(n-1, k) + T(n-1, k-2)     else: return T(n-1, k) + T(n-1, k-1) + T(n-1, k-2) @CachedFunction def a(n): return sum( T(n, k)*T(n, 2*n-k) for k in (0..2*n) ) [a(n) for n in (0..40)] # G. C. Greubel, Dec 22 2021 CROSSREFS Cf. A026519, A026520, A026521, A026522, A026523, A026524, A026525, A026526, A026527, A026528, A026529, A026530, A026531, A026532, A026533, A026534, A027263, A027264, A027265, A027266. Sequence in context: A000825 A273433 A132517 * A062358 A110385 A333898 Adjacent sequences:  A027259 A027260 A027261 * A027263 A027264 A027265 KEYWORD nonn AUTHOR EXTENSIONS More terms from Sean A. Irvine, Oct 26 2019 STATUS approved

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Last modified January 22 12:12 EST 2022. Contains 350481 sequences. (Running on oeis4.)