21971920 has 40 divisors (see below), whose sum is σ = 51324840. Its totient is φ = 8747520.

The previous prime is 21971903. The next prime is 21971927. The reversal of 21971920 is 2917912.

It can be written as a sum of positive squares in 4 ways, for example, as 219024 + 21752896 = 468^2 + 4664^2 .

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21971927) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 21010 + ... + 22030.

It is an arithmetic number, because the mean of its divisors is an integer number (1283121).

Almost surely, 2^21971920 is an apocalyptic number.

21971920 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21971920 is an abundant number, since it is smaller than the sum of its proper divisors (29352920).

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

21971920 is a wasteful number, since it uses less digits than its factorization.

21971920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1303 (or 1297 counting only the distinct ones).

The product of its (nonzero) digits is 2268, while the sum is 31.

The square root of 21971920 is about 4687.4214660088. The cubic root of 21971920 is about 280.0846682724.

The spelling of 21971920 in words is "twenty-one million, nine hundred seventy-one thousand, nine hundred twenty".