21720398 has 16 divisors (see below), whose sum is σ = 38436864. Its totient is φ = 9008280.

The previous prime is 21720389. The next prime is 21720409. The reversal of 21720398 is 89302712.

It is a congruent number.

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, 24590 + ... + 25457.

It is an arithmetic number, because the mean of its divisors is an integer number (2402304).

Almost surely, 2^21720398 is an apocalyptic number.

21720398 is a deficient number, since it is larger than the sum of its proper divisors (16716466).

21720398 is a wasteful number, since it uses less digits than its factorization.

21720398 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 50087.

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 21720398 is about 4660.5147784338. The cubic root of 21720398 is about 279.0118141818.

The spelling of 21720398 in words is "twenty-one million, seven hundred twenty thousand, three hundred ninety-eight".