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

1,1

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

Links

Table of n, a(n) for n=1..13.

Eric Weisstein's World of Mathematics, Pyramidal Number

Index to sequences related to pyramidal numbers

Example

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).

Crossrefs

Cf. A063778, A080851, A261720, A333915.

Sequence in context: A067142 A145453 A346754 * A264564 A304963 A034730

Adjacent sequences: A333913 A333914 A333915 * A333917 A333918 A333919

Keyword

nonn,more

Author

Ilya Gutkovskiy, Apr 09 2020

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

Status

approved