21001211220 has 96 divisors (see below), whose sum is σ = 66938296320. Its totient is φ = 4869842560.

The previous prime is 21001211111. The next prime is 21001211261. The reversal of 21001211220 is 2211210012.

It is a Harshad number since it is a multiple of its sum of digits (12).

It is a junction number, because it is equal to n+sod(n) for n = 21001211196 and 21001211205.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 676560 + ... + 706919.

It is an arithmetic number, because the mean of its divisors is an integer number (697273920).

Almost surely, 2^21001211220 is an apocalyptic number.

21001211220 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21001211220 is an abundant number, since it is smaller than the sum of its proper divisors (45937085100).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21001211220 is a wasteful number, since it uses less digits than its factorization.

21001211220 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1383525 (or 1383523 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 12.

Adding to 21001211220 its reverse (2211210012), we get a palindrome (23212421232).

It can be divided in two parts, 21001 and 211220, that added together give a triangular number (232221 = T₆₈₁).

The spelling of 21001211220 in words is "twenty-one billion, one million, two hundred eleven thousand, two hundred twenty".