A333914 a(n) is the least integer m >= 3 such that n is m-gonal pyramidal number.

3, 4, 5, 6, 7, 8, 3, 10, 11, 12, 4, 14, 15, 16, 5, 18, 3, 20, 6, 22, 23, 24, 7, 26, 27, 28, 4, 30, 31, 32, 9, 3, 35, 36, 10, 38, 5, 40, 11, 42, 43, 44, 12, 46, 47, 48, 6, 50, 51, 52, 14, 4, 3, 56, 15, 58, 7, 60, 16, 62, 63, 64, 17, 66, 67, 68, 8, 70, 71, 72, 19, 5, 75, 76, 20, 78, 9

Offset

4,1

Links

Table of n, a(n) for n=4..80.

Eric Weisstein's World of Mathematics, Pyramidal Number

Index to sequences related to pyramidal numbers

Example

a(18) = 5 since 18 is a pentagonal pyramidal number, but not a square pyramidal or tetrahedral number.

Crossrefs

Cf. A080851, A176774, A261720.

Sequence in context: A154660 A004492 A360663 * A140255 A050270 A202307

Adjacent sequences: A333911 A333912 A333913 * A333915 A333916 A333917

Keyword

nonn

Author

Ilya Gutkovskiy, Apr 09 2020

Status

approved