21221766720 has 1400 divisors, whose sum is σ = 99170995968. Its totient is φ = 4267468800.

The previous prime is 21221766703. The next prime is 21221766721. The reversal of 21221766720 is 2766712212.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21221766721) by changing a digit.

It is a polite number, since it can be written in 199 ways as a sum of consecutive naturals, for example, 684573105 + ... + 684573135.

Almost surely, 2^21221766720 is an apocalyptic number.

21221766720 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21221766720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (49585497984).

21221766720 is an abundant number, since it is smaller than the sum of its proper divisors (77949229248).

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

21221766720 is an equidigital number, since it uses as much as digits as its factorization.

21221766720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99 (or 59 counting only the distinct ones).

The product of its (nonzero) digits is 28224, while the sum is 36.

The spelling of 21221766720 in words is "twenty-one billion, two hundred twenty-one million, seven hundred sixty-six thousand, seven hundred twenty".