21720377 has 6 divisors (see below), whose sum is σ = 25266618. Its totient is φ = 18617424.

The previous prime is 21720371. The next prime is 21720389. The reversal of 21720377 is 77302712.

It can be written as a sum of positive squares in only one way, i.e., 13402921 + 8317456 = 3661^2 + 2884^2 .

It is not a de Polignac number, because 21720377 - 2⁸ = 21720121 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720371) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 221588 + ... + 221685.

It is an arithmetic number, because the mean of its divisors is an integer number (4211103).

Almost surely, 2^21720377 is an apocalyptic number.

It is an amenable number.

21720377 is a deficient number, since it is larger than the sum of its proper divisors (3546241).

21720377 is an equidigital number, since it uses as much as digits as its factorization.

21720377 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 443287 (or 443280 counting only the distinct ones).

The product of its (nonzero) digits is 4116, while the sum is 29.

The square root of 21720377 is about 4660.5125254633. The cubic root of 21720377 is about 279.0117242625.

The spelling of 21720377 in words is "twenty-one million, seven hundred twenty thousand, three hundred seventy-seven".