A333916 a(n) is the least integer that is pyramidal in exactly n ways.

4, 10, 30, 550, 1540, 48070, 223300, 2634940, 402610950, 1570545340, 13960282700, 5677137442900, 248297918605660

Offset: 1

Author

Ilya Gutkovskiy, Apr 09 2020

Keywords

• nonn
• more

Comments

a(n) has exactly n representations as an m-gonal pyramidal number P(m, k) = k*(k + 1)*(k*(m - 2) - m + 5) / 6, with m > 2, k > 1.

a(12) > 5*10^11. - Giovanni Resta, Apr 11 2020

Examples

			a(3) = 30 because 30 is the least integer which is pyramidal in 3 ways (30 is the fourth square pyramidal number, the third octagonal pyramidal number and also the second 31-gonal pyramidal number).
		

Links

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

Crossrefs

Cf. A063778, A080851, A261720, A333915.

Extensions

a(9) from Jinyuan Wang, Apr 10 2020

a(10)-a(11) from Giovanni Resta, Apr 10 2020

a(12)-a(13) from Bert Dobbelaere, Apr 12 2020