A225070 - OEIS

%I #9 Nov 12 2014 10:34:02

%S 10,69300,9729720,4257000,967412160,4104100000,1408951239696000,

%T 59860503846000000,1542547619019487080000,39054496014386012160000,

%U 450510331438947780000000

%N Least decagonal (10-gonal) number that is the product of n decagonal numbers greater than 1.

%H Lars Blomberg, <a href="/A225070/a225070.txt">Table of n, a(n) with solutions for n=1..11</a>

%e Let dec(n) = n*(4n-3). Then

%e a(1) = 10 = dec(2).

%e a(2) = 69300 = dec(132) = dec(2) * dec(42).

%e a(3) = 9729720 = dec(1560) = dec(3) * dec(4) * dec(42).

%e a(4) = 4257000 = dec(1032) = dec(2)^3 * dec(33).

%e a(5) = 967412160 = dec(15552) = dec(2) * dec(3) * dec(4) * dec(8) * dec(9).

%e a(6) = 4104100000 = dec(32032) = dec(2)^3 * dec(4) * dec(7) * dec(11).

%Y Cf. A001107 (decagonal numbers).

%Y Cf. A212616, A212617, A225066-A225069 (3-, 5- to 9-gonal cases).

%K nonn,more

%O 1,1

%A _T. D. Noe_, May 01 2013

%E Corrected a(6) and added a(7)-a(11) by _Lars Blomberg_, Sep 20 2013