20921977440 has 576 divisors, whose sum is σ = 89221257216. Its totient is φ = 4346597376.

The previous prime is 20921977387. The next prime is 20921977441. The reversal of 20921977440 is 4477912902.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (45).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (20921977441) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 8778489 + ... + 8780871.

It is an arithmetic number, because the mean of its divisors is an integer number (154898016).

Almost surely, 2^20921977440 is an apocalyptic number.

20921977440 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 20921977440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (44610628608).

20921977440 is an abundant number, since it is smaller than the sum of its proper divisors (68299279776).

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

20921977440 is a wasteful number, since it uses less digits than its factorization.

20921977440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2491 (or 2480 counting only the distinct ones).

The product of its (nonzero) digits is 254016, while the sum is 45.

The spelling of 20921977440 in words is "twenty billion, nine hundred twenty-one million, nine hundred seventy-seven thousand, four hundred forty".