720945

Appears in sequences

• Positive integers n such that n^2 = (x^4 - y^4)*(z^4 - t^4) where x>y and z>t are distinct pairs of integers with gcd(x,y)=gcd(z,t)=1.at n=27A147856
• a(n) is defined by the condition that the decimal expansion of Sum_{n>0} 1/a(n)^n = 1/a(1)^1 + 1/a(2)^2 + 1/a(3)^3 + ... begins with the concatenation of these numbers; also a(1) = 3 and a(n) > a(n-1).at n=10A324222