A218151 a(n) = 2*3^n*5^(n*(n-1)/2).

2, 6, 90, 6750, 2531250, 4746093750, 44494628906250, 2085685729980468750, 488832592964172363281250, 572850694879889488220214843750, 3356547040311852470040321350097656250, 98336339071636302833212539553642272949218750

Offset

0,1

Comments

a(n) = a(0)*Product_{i = 1..k} r(i)^C(n,i), with C(n,i) = 0 for all i > n. This is a special case of the geometric-geometric sequence having finite ratios, that is, k consecutive rows of ratios, whose first terms are r(1), r(2), r(3), ..., r(k), the last row (k-th row) being of a constant ratio, with k = 2, a(0) = 2, r(1) = 3, r(2) = 5.

Links

Table of n, a(n) for n=0..11.

Formula

a(n) = a(n-1)*3*5^(n-1), a(0) = 2.

Example

a(3) = 6750 because a(3) = 2*3^3*5^(3*2/2) = 2*3^3*5^3 = 2*27*125 = 6750.

Mathematica

RecurrenceTable[{a[0]==2, a[n]==a[n-1]3*5^(n-1)}, a, {n, 20}] (* Harvey P. Dale, Jul 30 2019 *)

Prog

(Maxima) A218151(n):=2*3^n*5^(n*(n-1)/2)$
makelist(A218151(n), n, 0, 11); /* Martin Ettl, Nov 03 2012 */

Crossrefs

Cf. A218148, A218149, A218150.

Sequence in context: A002432 A087277 A177861 * A343021 A007188 A376408

Adjacent sequences: A218148 A218149 A218150 * A218152 A218153 A218154

Keyword

nonn

Author

Mokhtar Mohamed, Oct 23 2012

Status

approved