Action of the irregular Hecke operator of index p on the theta-series of a quadratic form

Let F be a positive-definite integral even matrix of even order. For an arbitrary prime number p and natural n one obtains an explicit expression for the image of the theta series of genus n of the matrix F, under the action of an irregular Hecke operator with index p, in the form of a linear combination of theta series.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 144, pp. 68–71, 1985.