# oblong number

An integer of the form $n\cdot (n+1)$ or ${n}^{2}+n$. The partial sum

$$\sum _{i=0}^{n}2i$$ |

works, too. From this it follows that one can also multiply the $n$th triangular number^{}. Plenty of other relations to various polygonal numbers^{} can be obtained.

The first few terms are 0, 2, 6, 12, 20, 30, 42, 56, 72, 90, 110, and are listed in A002378 of Sloane’s OEIS.

Title | oblong number |
---|---|

Canonical name | OblongNumber |

Date of creation | 2013-03-22 15:50:19 |

Last modified on | 2013-03-22 15:50:19 |

Owner | CompositeFan (12809) |

Last modified by | CompositeFan (12809) |

Numerical id | 4 |

Author | CompositeFan (12809) |

Entry type | Definition |

Classification | msc 11D85 |

Synonym | heteromecic number |

Synonym | pronic number |