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

Author

Ilya Gutkovskiy, Apr 09 2020

Keywords

• nonn

Examples

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

Links

• Eric Weisstein's World of Mathematics, Pyramidal Number
• Index to sequences related to pyramidal numbers

Crossrefs

Cf. A080851, A176774, A261720.