21891870 has 256 divisors, whose sum is σ = 79349760. Its totient is φ = 4199040.

The previous prime is 21891853. The next prime is 21891871. The reversal of 21891870 is 7819812.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21891871) by changing a digit.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 1683984 + ... + 1683996.

It is an arithmetic number, because the mean of its divisors is an integer number (309960).

Almost surely, 2^21891870 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21891870, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (39674880).

21891870 is an abundant number, since it is smaller than the sum of its proper divisors (57457890).

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

21891870 is a wasteful number, since it uses less digits than its factorization.

21891870 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 59 (or 41 counting only the distinct ones).

The product of its (nonzero) digits is 8064, while the sum is 36.

The square root of 21891870 is about 4678.8748647511. The cubic root of 21891870 is about 279.7441114560.

The spelling of 21891870 in words is "twenty-one million, eight hundred ninety-one thousand, eight hundred seventy".