A304780 - OEIS

A304780

Consider a triangle whose first row is {1,2} and, for n > 1, has as its n-th row the integers k through 2k where k is the sum of the numbers in the (n-1)th row. Then a(n) is the first number in the n-th row.

1, 3, 18, 513, 395523, 234658258578, 82596747478641253260993, 10233334041075645341729789249315281196742910563, 157081688394356396673208173772909833928515988895188885472258972148661958252271815996039831298

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,2

LINKS

Table of n, a(n) for n=1..9.

FORMULA

a(1) = 1, a(n) = (3*a(n-1)*(a(n-1) + 1))/2 for n > 1.

a(n) ~ (2/3) * c^(2^n), where c = 1.515006464529590220430714781603262955960312205695360166833... - Vaclav Kotesovec, Jul 23 2018

EXAMPLE

Triangle begins:

1, 2; (row sum = 3)

3, 4, 5, 6; (row sum = 18)