There are (at least) three types of Euler transforms (or transformations). The first is a set of transformations of hypergeometric functions, called Euler's hypergeometric transformations.
The second type of Euler transform is a technique for series convergence improvement which takes a convergent alternating series
(1)
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into a series with more rapid convergence to the same value to
(2)
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where the forward difference is defined by
(3)
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(Abramowitz and Stegun 1972; Beeler et al. 1972). Euler's hypergeometric and convergence improvement transformations are related by the fact that when is taken in the second of Euler's hypergeometric transformations
(4)
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where is a hypergeometric function, it gives Euler's convergence improvement transformation of the series (Abramowitz and Stegun 1972, p. 555).
The third type of Euler transform is a relationship between certain types of integer sequences (Sloane and Plouffe 1995, pp. 20-21). If , , ... and , , ... are related by
(5)
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or, in terms of generating functions and ,
(6)
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then is said to be the Euler transform of (Sloane and Plouffe 1995, p. 20). The Euler transform can be effected by introducing the intermediate series , , ... given by
(7)
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then
(8)
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with . Similarly, the inverse transform can be effected by computing the intermediate series as
(9)
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then
(10)
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where is the Möbius function.
In graph theory, if is the number of unlabeled connected graphs on nodes satisfying some property, then is the total number of unlabeled graphs (connected or not) with the same property. This application of the Euler transform is called Riddell's formula for unlabeled graph (Sloane and Plouffe 1995, p. 20).
There are also important number theoretic applications of the Euler transform. For example, if there are kinds of parts of size 1, kinds of parts of size 2, etc., in a given type of partition, then the Euler transform of is the number of partitions of into these integer parts. For example, if for all , then is the number of partitions of into integer parts. Similarly, if for prime and for composite, then is the number of partitions of into prime parts (Sloane and Plouffe 1995, p. 21). Other applications are given by Andrews (1986), Andrews and Baxter (1989), and Cameron (1989).