75440domain: NAppears in sequences9-gonal (or enneagonal) pyramidal numbers: a(n) = n*(n+1)*(7*n-4)/6.at n=40A007584Icosagonal numbers divisible by 20.at n=19A117798Icosagonal numbers for which the sum of the digits is also an icosagonal number.at n=7A117799Even 9-gonal (nonagonal) pyramidal numbers.at n=29A218329