21811972 has 48 divisors (see below), whose sum is σ = 48520192. Its totient is φ = 8346240.

The previous prime is 21811957. The next prime is 21811987. The reversal of 21811972 is 27911812.

It is an interprime number because it is at equal distance from previous prime (21811957) and next prime (21811987).

It is a Harshad number since it is a multiple of its sum of digits (31).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10318 + ... + 12250.

Almost surely, 2^21811972 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21811972, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24260096).

21811972 is an abundant number, since it is smaller than the sum of its proper divisors (26708220).

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

21811972 is a wasteful number, since it uses less digits than its factorization.

21811972 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1988 (or 1986 counting only the distinct ones).

The product of its digits is 2016, while the sum is 31.

The square root of 21811972 is about 4670.3288963412. The cubic root of 21811972 is about 279.4033724586.

The spelling of 21811972 in words is "twenty-one million, eight hundred eleven thousand, nine hundred seventy-two".