Hosta

A centered tetrahedral number is a centered figurate number that represents a tetrahedron. The centered tetrahedral number for a specific n is given by

The first such numbers are 1, 5, 15, 35, 69, 121, 195, 295, 425, 589, 791, ... (sequence A005894 in the OEIS).

Parity and divisibility

• Every centered tetrahedral number is odd.
• Every centered tetrahedral number with an index of 2, 3 or 4 modulo 5 is divisible by 5.

References

• Deza, E.; Deza, M. (2012). Figurate Numbers. Singapore: World Scientific Publishing. pp. 126–128. ISBN 978-981-4355-48-3.