Definition of triangular number in US English:

triangular number


  • Any of the series of numbers (1, 3, 6, 10, 15, etc.) obtained by continued summation of the natural numbers 1, 2, 3, 4, 5, etc.

    • ‘The first sequence is known as the triangular numbers.’
    • ‘Pythagoras studied properties of numbers which would be familiar to mathematicians today, such as even and odd numbers, triangular numbers, perfect numbers etc.’
    • ‘His work on triangular numbers inspired Sierpinski to further work on this topic while Zarankiewicz also worked jointly with Kuratowski on topology.’
    • ‘This triangle has an elementary use in probability and combinatorics, and both the series of triangular numbers and the Fibonacci series can be derived from it.’
    • ‘The triangular numbers and the Fibonacci numbers can be found in Pascal's triangle.’