21981840 has 40 divisors (see below), whose sum is σ = 68144448. Its totient is φ = 5861760.

The previous prime is 21981823. The next prime is 21981871. The reversal of 21981840 is 4818912.

It is a tau number, because it is divible by the number of its divisors (40).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 45556 + ... + 46035.

Almost surely, 2^21981840 is an apocalyptic number.

21981840 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21981840 is an abundant number, since it is smaller than the sum of its proper divisors (46162608).

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

21981840 is a wasteful number, since it uses less digits than its factorization.

21981840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 91607 (or 91601 counting only the distinct ones).

The product of its (nonzero) digits is 4608, while the sum is 33.

The square root of 21981840 is about 4688.4794976623. The cubic root of 21981840 is about 280.1268133053.

The spelling of 21981840 in words is "twenty-one million, nine hundred eighty-one thousand, eight hundred forty".