21901638 has 16 divisors (see below), whose sum is σ = 47785536. Its totient is φ = 6636840.

The previous prime is 21901637. The next prime is 21901639. The reversal of 21901638 is 83610912.

It is an interprime number because it is at equal distance from previous prime (21901637) and next prime (21901639).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21901631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 165856 + ... + 165987.

It is an arithmetic number, because the mean of its divisors is an integer number (2986596).

Almost surely, 2^21901638 is an apocalyptic number.

21901638 is an abundant number, since it is smaller than the sum of its proper divisors (25883898).

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

21901638 is a wasteful number, since it uses less digits than its factorization.

21901638 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 331859.

The product of its (nonzero) digits is 2592, while the sum is 30.

The square root of 21901638 is about 4679.9185890355. The cubic root of 21901638 is about 279.7857118943.

It can be divided in two parts, 2190 and 1638, that added together give a triangular number (3828 = T₈₇).

The spelling of 21901638 in words is "twenty-one million, nine hundred one thousand, six hundred thirty-eight".