Congruum

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For the female singular in ecclesiastical context see congrua portio

A congruum (plural congrua) is a number h ∈ Z which satisfies the congruum problem, that is, satisfies the two equations x² + h = a² and x² - h = b² for some x, a, b ∈ Z.

The first few congrua (sequence A057102 in OEIS) are: 24, 96, 120, 240, 336, 384, 480, 720,...