

A338105


a(n) is the least integer that can be expressed as the difference of two ngonal numbers in exactly n ways.


2



9, 96, 1330, 4725, 21021, 22400, 421515, 675675, 5370365, 576576, 10790325, 39255125, 51548805, 7286400, 978624647, 144729585, 649593945, 125245120, 1109593485, 4519064403, 13908638315, 253955520, 8860666815, 30587913125, 33144736086, 859541760, 147839441750
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OFFSET

3,1


COMMENTS

a(17) <= 1340770739, a(18) = 144729585, a(19) <= 9381302307, a(20) <= 1257818848, a(21) <= 6299438145, a(22) <= 32911706919, a(23) <= 26720105555, a(24) <= 3141537984, a(25) <= 59558175105, a(26) <= 71119743695, a(27) <= 260207700831, a(28) <= 28582652736, a(29) <= 688883385190, a(30) <= 593086020813.  Chai Wah Wu, Oct 14 2020


LINKS

Martin Ehrenstein, Table of n, a(n) for n = 3..40
Eric Weisstein's World of Mathematics, Polygonal Number
Index to sequences related to polygonal numbers


EXAMPLE

a(3) = 9 because 9 = 10  1 = 15  6 = 45  36 and this is the least integer that can be expressed as the difference of two triangular numbers in exactly 3 ways.


CROSSREFS

Cf. A038547, A068314, A072502, A257411, A334034, A334035, A334036, A334037.
Sequence in context: A264208 A070896 A081131 * A331113 A158489 A069636
Adjacent sequences: A338102 A338103 A338104 * A338106 A338107 A338108


KEYWORD

nonn


AUTHOR

Ilya Gutkovskiy, Oct 10 2020


EXTENSIONS

a(11)a(16) from Chai Wah Wu, Oct 13 2020
a(17) and a(19)a(40) from Martin Ehrenstein, Oct 23 2020


STATUS

approved



