It is a happy number.
621621020 is digitally balanced in base 6, because in such base it contains all the possibile digits an equal number of times.
It is a congruent number.
It is an unprimeable number.
Almost surely, 2621621020 is an apocalyptic number.
It is an amenable number.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
621621020 is a wasteful number, since it uses less digits than its factorization.
621621020 is an evil number, because the sum of its binary digits is even.
The square root of 621621020 is about 24932.3288122069. The cubic root of 621621020 is about 853.4443950634. Note that the first 3 decimals are identical.
Adding to 621621020 its reverse (20126126), we get a palindrome (641747146).
The spelling of 621621020 in words is "six hundred twenty-one million, six hundred twenty-one thousand, twenty".