A167683 -id:A167683 - cp's OEIS frontend

A007325 G.f.: Product_{k>0} (1-x^(5k-1))(1-x^(5k-4))/((1-x^(5k-2))(1-x^(5k-3))).

1, -1, 1, 0, -1, 1, -1, 1, 0, -1, 2, -3, 2, 0, -2, 4, -4, 3, -1, -3, 6, -7, 5, 0, -5, 9, -10, 7, -1, -7, 14, -16, 11, -1, -11, 20, -22, 16, -2, -15, 29, -33, 23, -2, -23, 41, -45, 32, -4, -30, 57, -64, 45, -4, -43, 78, -86, 60, -7, -57, 107, -119, 83, -8, -79, 143

Offset: 0

N. J. A. Sloane, Mira Bernstein

Expansion of f(-x, -x^4) / f(-x^2, -x^3) in powers of x where f(,) is Ramanujan's two-variable theta function.
Hauptmodul series for Gamma(5).
Expansion of Rogers-Ramanujan's continued fraction 1 / (1 + x / ( 1 + x^2 / ( 1 + x^3 / ( 1 + x^4 / ... )))).
Given the g.f. A(x) the notation R(q) := q^(1/5) * A(q) is used by Berndt.

			G.f. = 1 - x + x^2 - x^4 + x^5 - x^6 + x^7 - x^9 + 2*x^10 - 3*x^11 + 2*x^12 - ...
G.f. = q - q^6 + q^11 - q^21 + q^26 - q^31 + q^36 - q^46 + 2*q^51 - 3*q^56 + ...

G. E. Andrews and B. C. Berndt, Ramanujan's Lost Notebook, Part I, Springer, 2005, see p. 57.
B. C. Berndt, Ramanujan's Notebooks Part V, Springer-Verlag, see p. 9.
J. M. Borwein and P. B. Borwein, Pi and the AGM, Wiley, 1987, p. 81.
A. Erdelyi, Higher Transcendental Functions, McGraw-Hill, 1955, Vol. 3, p. 24.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).

Seiichi Manyama, Table of n, a(n) for n = 0..10000 (terms 0..1000 from T. D. Noe)
G. E. Andrews, Simplicity and surprise in Ramanujan's "Lost" Notebook, Amer. Math. Monthly, 104 (No. 10, Dec. 1997), 918-925.
W. Duke, Continued fractions and modular functions, Bull. Amer. Math. Soc. 42 (2005), 137-162; see Eq. (6.4).
G. S. Joyce, Exact results for the activity and thermal compressibility of the hard-hexagon model, J. Phys. A 21 (1988), L983-L988.
J. Malenfant, Generalizing Ramanujan's J Functions, arXiv preprint arXiv:1109.5957 [math.NT], 2011.
P. J. Nahin, Number-Crunching, Princeton University Press, 2011. See p. 22 equation (2.2.4).
Michael Somos, Introduction to Ramanujan theta functions
Eric Weisstein's World of Mathematics, Ramanujan Theta Functions
Eric Weisstein's World of Mathematics, Rogers-Ramanujan Continued Fraction.

Cf. A055101, A055102, A055103, A003823, A167683.

t1:=mul((1-x^(5*k-1))*(1-x^(5*k-4))/((1-x^(5*k-2))*(1-x^(5*k-3))), k=1..60); seriestolist(series(t1,x,59)); # N. J. A. Sloane, Jun 10 2013
A007325_G:=proc(x,NK);Digits:=250;
Q2:=1;
for k from NK by -1 to 0 do
Q1:=1+x^k/Q2; Q2:=Q1; od;
Q3:=Q2; S:=Q3-1;
end;
# Sergei N. Gladkovskii, Dec 18 2011

a[ n_] := SeriesCoefficient[ QPochhammer[ q, q^5] QPochhammer[ q^4, q^5] / (QPochhammer[ q^2, q^5] QPochhammer[ q^3, q^5]), {q, 0, n}]; (* Michael Somos, Aug 17 2011 *)
a[ n_] := SeriesCoefficient[ ContinuedFractionK[ q^k, 1, {k, 0, n}], {q, 0, n}]; (* Michael Somos, Jun 10 2013 *)
max = 65; CoefficientList[ Series[ Fold[ #2/(1 + #1)&, q^n, q^Reverse[ Range[0, max-1] ] ], {q, 0, max}], q] (* Jean-François Alcover, Apr 04 2013 *)

{a(n) = my(k); if( n<0, 0, k = (3 + sqrtint(9 + 40*n)) \ 10; polcoeff( sum( n=-k, k, (-1)^n * x^((5*n^2 + 3*n)/2), x * O(x^n)) / sum( n=-k, k,( -1)^n * x^((5*n^2 + n)/2), x * O(x^n)), n))};

{a(n) = if( n<0, 0, polcoeff( prod( k=1, n, if(k%5, (1 - x^k)^((-1)^binomial( k%5, 2)), 1), 1 + x * O(x^n)), n))};

{a(n) = my(cf); if( n<0, 0, cf = contfracpnqn( matrix( 2, (sqrtint(8*n + 1) + 1)\2, i, j, if( i==1, x^(j-1), 1))); polcoeff( cf[2, 1] / cf[1, 1] + x * O(x^n), n))};

{a(n) = my(A, m); if( n<0, 0, m=1; A = 1 + O(x); while( m<=n, m*=5; A = x * subst(A, x, x^5); A = (A * (1 - 2*A + 4*A^2 - 3*A^3 + A^4) / (1 + 3*A + 4*A^2 + 2*A^3 + A^4) / x)^(1/5)); polcoeff(A, n))};

Euler transform of period 5 sequence [-1, 1, 1, -1, 0, ...] (=-A080891).
G.f.: Product_{k>=1}(1-x^(5*k-1)) * (1-x^(5*k-4)) / ( (1-x^(5*k-2)) * (1-x^(5*k-3)) ) = H(x) / G(x) where H and G are respectively the g.f. of A003114 and A003106.
G.f.: (Sum (-1)^k x^((5*k + 3)*k/2))/(Sum (-1)^k x^((5*k + 1)*k/2)). - Michael Somos, Dec 13 2002
Given g.f. A(x), then B(q) = q * A(q^5) satisfies 0 = f(B(q), B(q^2)) where f(u, v) = u^2 - v + u*v^3 + u^3*v^2. - Michael Somos, Mar 09 2004
Given g.f. A(x), then B(q) = q * A(q^5) satisfies 0 = f(B(q), B(q^2), B(q^4)) where f(u, v, w) = u * (u*v + w^2 + v^2*w) - w. - Michael Somos, Aug 29 2005
Given g.f. A(x), then B(q) = q * A(q^5) satisfies 0 = f(B(q), B(q^2), B(q^3), B(q^6)) where f(u1, u2, u3, u6) = u1*u2 + u1*u3^2*u6 + u2*u3^2 - u2^2*u3*u6 - u3. - Michael Somos, Aug 29 2005
G.f.: 1 / (1 + x / ( 1 + x^2 / ( 1 + x^3 / ( 1 + x^4 / ... )))).
G.f.: 1 / (1 + 1 / (x^-1 + 1 / (x^-1 + 1 / (x^-2 + 1 / (x^-2 + 1 / ... ))))). - Michael Somos, Apr 30 2012
G.f.: A(x) =  S(0) -1; S(k) = 1 + x^k/S(k+1); (continued fraction). - Sergei N. Gladkovskii, Dec 18 2011
Hankel transform is A167683. - Michael Somos, Apr 30 2012
a(n) = (-1)^n * A226556(n). - Michael Somos, Jun 11 2013
a(0) = 1, a(n) = -(1/n)*Sum_{k=1..n} A109091(k)*a(n-k) for n > 0. - Seiichi Manyama, Apr 01 2017

A131723 a(2n) = 1-n^2, a(2n+1) = n*(n+1).

Original entry on oeis.org

0, 2, -3, 6, -8, 12, -15, 20, -24, 30, -35, 42, -48, 56, -63, 72, -80, 90, -99, 110, -120, 132, -143, 156, -168, 182, -195, 210, -224, 240, -255, 272, -288, 306, -323, 342, -360, 380, -399, 420, -440, 462, -483, 506, -528, 552, -575, 600, -624, 650, -675

Offset: 0

Paul Curtz, Sep 16 2007

See A167683 for link to Hankel transform of A007325. Partial sum of signed version of A000096. [Paul Barry, Nov 09 2009]

Vincenzo Librandi, Table of n, a(n) for n = 0..10000
Index entries for linear recurrences with constant coefficients, signature (-2,0,2,1).

Cf. A000096, A002378, A005563, A007325, A167683.

[-(-1)^n*(2*n^2+8*n+3-3*(-1)^n)/8: n in [0..50]]; // Vincenzo Librandi, Aug 10 2011

A131723:=n->-(-1)^n*floor((n+1)*(n+3)/4): seq(A131723(n), n=0..100); # Wesley Ivan Hurt, Jun 07 2016

Table[-(-1)^n*Floor[(n + 1)*(n + 3)/4], {n, 0, 100}] (* Wesley Ivan Hurt, Jun 07 2016 *)

From Paul Barry, Nov 09 2009: (Start)
G.f.: x*(2+x)/((1+x)^3*(1-x)).
a(n) = -(-1)^n*(2*n^2+8*n+3-3*(-1)^n)/8. (End)
From Wesley Ivan Hurt, Jun 07 2016: (Start)
a(n) = -2*a(n-1) + 2*a(n-3) + a(n-4) for n>3.
a(n) = -(-1)^n*floor((n+1)*(n+3)/4).
a(2k) = - A005563(k), a(2k-1) = A002378(k) for k>0. (End)

More terms from Vincenzo Librandi, Aug 10 2011

cp's OEIS Frontend

A167687 a(n)=A167683(n)-A167686(n).

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A007325 G.f.: Product_{k>0} (1-x^(5k-1))(1-x^(5k-4))/((1-x^(5k-2))(1-x^(5k-3))).

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A131723 a(2n) = 1-n^2, a(2n+1) = n*(n+1).

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A167686 Hankel transform of A003823.

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cp's OEIS Frontend

A167687 a(n)=A167683(n)-A167686(n).

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A007325 G.f.: Product_{k>0} (1-x^(5k-1))*(1-x^(5k-4))/((1-x^(5k-2))*(1-x^(5k-3))).

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PARI

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A131723 a(2*n) = 1-n^2, a(2*n+1) = n*(n+1).

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Magma

Maple

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A167686 Hankel transform of A003823.

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A007325 G.f.: Product_{k>0} (1-x^(5k-1))(1-x^(5k-4))/((1-x^(5k-2))(1-x^(5k-3))).

A131723 a(2n) = 1-n^2, a(2n+1) = n*(n+1).