(number theory) An odd natural number k such that k⨯2ⁿ+1 is composite for all natural numbers n.

(UK politics, colloquial) Synonym of 11 Downing Street

(mathematical analysis, nonstandard analysis) A hyperreal number which is not a real number.

plural of taxicab number

plural of Carmichael number

plural of Heegner number

(mathematics) The nth taxicab number, typically denoted Ta(n) or Taxicab(n), is the smallest number that can be expressed as a sum of two positive algebraic cubes in n distinct ways.

(mathematics) A composite number n that satisfies the modular arithmetic congruence relation bⁿ⁻¹≡1(mod n) for all integers 1<b<n that are relatively prime to n.

(mathematics) A squarefree positive integer d such that the imaginary quadratic field Q(√(−d)) has class number 1; equivalently, such that its ring of integers has unique factorization.

Any of many games based upon numbers.