21981492 has 54 divisors (see below), whose sum is σ = 60183942. Its totient is φ = 6761664.

The previous prime is 21981469. The next prime is 21981497. The reversal of 21981492 is 29418912.

It can be written as a sum of positive squares in 3 ways, for example, as 3006756 + 18974736 = 1734^2 + 4356^2 .

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 (21981497) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 4278 + ... + 7890.

Almost surely, 2^21981492 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 21981492, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30091971).

21981492 is an abundant number, since it is smaller than the sum of its proper divisors (38202450).

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

21981492 is a wasteful number, since it uses less digits than its factorization.

21981492 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3649 (or 3631 counting only the distinct ones).

The product of its digits is 10368, while the sum is 36.

The square root of 21981492 is about 4688.4423852704. The cubic root of 21981492 is about 280.1253350450.

The spelling of 21981492 in words is "twenty-one million, nine hundred eighty-one thousand, four hundred ninety-two".