A090907 Ratio of products of successive rows of the irregular triangle defined in A090905.

2, 6, 140, 1287, 2139552000, 2949442889323392, 322686644032484531917367528014184448000000

Offset: 1

Author

Amarnath Murthy, Dec 13 2003

Keywords

• nonn

Comments

Conjecture: For n > 4 the last term of the n-th group is 2p where p is the largest prime in the (n-1)th group. And these are the Bertrand primes.

Examples

			a(1)=(2!/1!)*(0!/1!)
a(2)=(4!/2!)*(1!/2!)
a(3)=(8!/4!)*(2!/4!)
a(4)=(14!/8!)*(4!/8!)
a(5)=(26!/14!)*(8!/14!)
a(6)=(46!/26!)*(14!/26!)
For n>=6 we have a(n)= ((2*A006992(n))!/(2*A006992(n-1))!)*((2*A006992(n-2))!/(2*A006992(n-1))!), verified for 4<n<21
		

Crossrefs

Cf. A090904, A090905, A090906.

Extensions

Edited by Mohammed Bouayoun (bouyao(AT)wanadoo.fr), Mar 05 2004