(mathematics) The number of possible lattice paths from the southwest corner (0, 0) of an n × n grid to the northeast corner (n, n), using only single steps north, northeast or east, and not rising above the southwest–northeast diagonal.

plural of Schröder number

(combinatorics) Any of the triangular array of natural numbers defined by N(n, k), n = 1, 2, 3 ..., 1 ≤ k ≤ n, occurring in various counting problems.

plural of Lychrel number

(mathematics) A natural number that cannot form a palindrome through the iterative process of repeatedly reversing its digits and adding the resulting numbers.

(number theory) A positive integer whose abundancy index is greater than that of any lesser positive integer. / Used other than figuratively or idiomatically: see superabundant, number.

plural of negative number

plural of positive number

plural of superabundant number

plural of book number