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 A090907 Ratio of products of successive rows of the irregular triangle defined in A090905. 4
 2, 6, 140, 1287, 2139552000, 2949442889323392, 322686644032484531917367528014184448000000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 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. LINKS Table of n, a(n) for n=1..7. EXAMPLE 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

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Last modified June 20 23:18 EDT 2024. Contains 373535 sequences. (Running on oeis4.)