1,2

a(n)=(1/6)*(10*n^3-9*n^2+5*n)

Cf. A004126 = alternate vertex; A000447 = structured diamonds; A100145 for more on structured numbers).

Adjacent sequences: A100176 A100177 A100178 this_sequence A100180 A100181 A100182

Sequence in context: A020163 A139275 A133547 this_sequence A106598 A014816 A000441

easy,nonn

James A. Record (james.record(AT)gmail.com). Nov 07, 2004.