OEIS/Infinite Products

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OEIS collection of transforms

weighout   b from a in 1+SUM b_n x^n = PI (1+x^n)^a_n
weighouti  a from b in 1+SUM b_n x^n = PI (1+x^n)^a_n
weighini   a from b in 1+SUM b_n x^n = PI (1+x^a_n)
weigh2out  b from a in 1+SUM b_n x^n = PI (x^-n+1+x^n)^a_n
weigh2outi a from b in 1+SUM b_n x^n = PI (x^-n+1+x^n)^a_n
weigh2in   b from a in 1+SUM b_n x^n = PI (x^-a_n+1+x^a_n)
weigh2ini  a from b in 1+SUM b_n x^n = PI (x^-a_n+1+x^a_n)

Programs

A046042 Number of partitions of n into fourth powers.

(Maple) 
g := -1 + 1/product(1 - x^(j^4), j=1..10): 
gser := series(g, x=0, 105): seq(coeff(gser, x, n), n=1..102);
(Maple, A303350)
seq(coeff(series(mul((1+4*x^k)^(1/2), k = 1..n), x, n+1), x, n), n=0..40);
(Mathematica) 
g = -1 + 1/Product[1 - x^(j^4), {j, 1, 10}]; 
gser = Series[g, {x, 0, 105}]; Table[Coefficient[gser, x, n], {n, 1, 102}]
(PARI, A322199)
{a(n) = polcoeff( 1/prod(m=1, n, 1 - (2^m+1)*x^m +x*O(x^n)), n)}
for(n=0, 30, print1(a(n), ","))

Generalized Euler transform

Product_{k>0} (1 - g(k)*x^k)^(- f(k)) = a(0) + a(1)*x + a(2)*x^2 + ...
  1. If we set g(n) = 1, we get the usual Euler transform.
  2. If we set f(n) = - h(n) and g(n) = -1, we get the weighout transform (cf. A026007).
  3. If we set f(n) = - n (A001478) and g(n) = n (A000027), we get A266964.
  4. With the default f(n) = g(n) = A000012 (all 1's), we get A000041 (number of partitions of n).

Interesting sequences

  • A000081 Euler transform of itself, shifted by 1