1 − 2 + 4 − 8 + ⋯ a convergent geometric series whose sum is by the usual formula. The Borel sum of is also ; when Émile Borel introduced the limit formulation of Borel summation in 1896, this was one of his first examples after 1 − 1 + 1 − 1 + ⋯ 1 − 2 + 4 − 8 + ⋯ In mathematics, is the infinite series whose terms are the successive powers of two with alternating signs. As a geometric series, it is characterized by its first term, 1, and its common ratio, −2. As a series of real numbers it diverges, so in
2-8-8-8-8-8-2 2-8-8-8-8-8-2 Under the Whyte notation for the classification of steam locomotives, a 2-8-8-8-8-8-2 has two leading wheels, five sets of eight driving wheels, and two trailing wheels. Because of its length, such a locomotive must be an articulated locomotive. It is not longer than a normal articulated; the fourth and fifth sets of drivers are located under the tender. Other equivalent classifications are: UIC classification: 1-D-D-D-D-D-1 (also known as German classification and Italian classification) AAR classification: 1-D-D-D-D-D-1 French classification: 140+040+040+040+041 Turkish classification: 45+44+44+44+45 Swiss classification: 4/5+4/4+4/4+4/4+4/5 The equivalent UIC classification is to be refined to (1'D)DDD(D1'). The Baldwin Locomotive Works