21591390 has 16 divisors (see below), whose sum is σ = 51819408. Its totient is φ = 5757696.

The previous prime is 21591389. The next prime is 21591413. The reversal of 21591390 is 9319512.

It is a Harshad number since it is a multiple of its sum of digits (30), and also a Moran number because the ratio is a prime number: 719713 = 21591390 / (2 + 1 + 5 + 9 + 1 + 3 + 9 + 0).

It is a Curzon number.

It is a zygodrome in base 9.

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, 359827 + ... + 359886.

It is an arithmetic number, because the mean of its divisors is an integer number (3238713).

Almost surely, 2^21591390 is an apocalyptic number.

21591390 is an abundant number, since it is smaller than the sum of its proper divisors (30228018).

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

21591390 is a wasteful number, since it uses less digits than its factorization.

21591390 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 719723.

The product of its (nonzero) digits is 2430, while the sum is 30.

The square root of 21591390 is about 4646.6536346063. The cubic root of 21591390 is about 278.4583213213.

The spelling of 21591390 in words is "twenty-one million, five hundred ninety-one thousand, three hundred ninety".