It is a happy number.
It is a congruent number.
It is an unprimeable number.
Almost surely, 2121200021000020 is an apocalyptic number.
121200021000020 is a gapful number since it is divisible by the number (10) formed by its first and last digit.
It is an amenable number.
It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.
121200021000020 is a wasteful number, since it uses less digits than its factorization.
121200021000020 is an evil number, because the sum of its binary digits is even.
Adding to 121200021000020 its reverse (20000120002121), we get a palindrome (141200141002141).
The spelling of 121200021000020 in words is "one hundred twenty-one trillion, two hundred billion, twenty-one million, twenty", and thus it is an aban number.