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 A118181 Row sums of triangle A118180: a(n) = Sum_{k=0..n} (3^k)^(n-k) for n>=0. 3
 1, 2, 5, 20, 137, 1622, 33293, 1182440, 72811793, 7757988842, 1433154521621, 458101483131260, 253879024041595289, 243453910296759945662, 404765167247068325944349, 1164432505878183620543030480 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Also equals column 0 of the matrix square of triangle A118180, where [A118180^2](n,k) = a(n-k)*(3^k)^(n-k) for n>=k>=0. LINKS G. C. Greubel, Table of n, a(n) for n = 0..90 FORMULA G.f.: A(x) = Sum_{n>=0} x^n/(1-3^n*x). EXAMPLE A(x) = 1/(1-x) + x/(1-3x) + x^2/(1-9x) + x^3/(1-27x) + ... = 1 + 2*x + 5*x^2 + 20*x^3 + 137*x^4 + 1622*x^5 + 33293*x^6 +... MAPLE seq( add(3^(k*(n-k)), k=0..n), n=0..30); # modified by G. C. Greubel, Jun 29 2021 MATHEMATICA Table[Sum[3^(k*(n-k)), {k, 0, n}], {n, 0, 30}] (* G. C. Greubel, Jun 29 2021 *) PROG (PARI) a(n)=sum(k=0, n, (3^k)^(n-k) ); (Magma) [(&+[3^(k*(n-k)): k in [0..n]]): n in [0..30]]; // G. C. Greubel, Jun 29 2021 (Sage) [sum(3^(k*(n-k)) for k in (0..n)) for n in (0..30)] # G. C. Greubel, Jun 29 2021 CROSSREFS Cf. A118180 (triangle), A118182 (antidiagonal sums); A118183, A118184. Sequence in context: A012317 A297630 A297629 * A140988 A136650 A229662 Adjacent sequences: A118178 A118179 A118180 * A118182 A118183 A118184 KEYWORD nonn AUTHOR Paul D. Hanna, Apr 15 2006 STATUS approved

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Last modified February 26 07:39 EST 2024. Contains 370335 sequences. (Running on oeis4.)