0,3

Geometrically, the partial sums of dodecahedral numbers may be interpreted as 4-dimensional dodecahedral hyperpyramidal numbers. It is somewhat surprising that this is (with proper offset) the triangular number of the "second pentagonal numbers, minus 1."

a(n) = SUM[i=0..n] A006566(i). a(n) = SUM[i=0..n] i*(3*i-1)*(3*i-2)/2. a(n+1) = A000217(A095794(n)). a(n+1) = A000217(A005449(n) - 1). a(n+1) = A000217((n*(3n+1)/2)-1). a(n+1) = A000217(A001844(n) - A000217(n+1) - 1).

Cf. A000217, A001844, A005449, A006566, A095794.

Sequence in context: A068142 A126229 A060537 this_sequence A068986 A077400 A041854

Adjacent sequences: A116686 A116687 A116688 this_sequence A116690 A116691 A116692

easy,nonn

Jonathan Vos Post (jvospost2(AT)yahoo.com), Mar 15 2006