21981372 has 48 divisors (see below), whose sum is σ = 59039232. Its totient is φ = 6235200.

The previous prime is 21981343. The next prime is 21981373. The reversal of 21981372 is 27318912.

It is a hoax number, since the sum of its digits (33) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981373) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11818 + ... + 13550.

It is an arithmetic number, because the mean of its divisors is an integer number (1229984).

Almost surely, 2^21981372 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 21981372, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29519616).

21981372 is an abundant number, since it is smaller than the sum of its proper divisors (37057860).

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

21981372 is a wasteful number, since it uses less digits than its factorization.

21981372 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1898 (or 1896 counting only the distinct ones).

The product of its digits is 6048, while the sum is 33.

The square root of 21981372 is about 4688.4295878258. The cubic root of 21981372 is about 280.1248252964.

It can be divided in two parts, 2198 and 1372, that added together give a triangular number (3570 = T₈₄).

The spelling of 21981372 in words is "twenty-one million, nine hundred eighty-one thousand, three hundred seventy-two".