21915990 has 48 divisors (see below), whose sum is σ = 57569616. Its totient is φ = 5784000.

The previous prime is 21915979. The next prime is 21916001. The reversal of 21915990 is 9951912.

It is an interprime number because it is at equal distance from previous prime (21915979) and next prime (21916001).

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 7885 + ... + 10295.

It is an arithmetic number, because the mean of its divisors is an integer number (1199367).

Almost surely, 2^21915990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21915990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28784808).

21915990 is an abundant number, since it is smaller than the sum of its proper divisors (35653626).

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

21915990 is a wasteful number, since it uses less digits than its factorization.

21915990 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2525 (or 2522 counting only the distinct ones).

The product of its (nonzero) digits is 7290, while the sum is 36.

The square root of 21915990 is about 4681.4516979245. The cubic root of 21915990 is about 279.8468124651.

The spelling of 21915990 in words is "twenty-one million, nine hundred fifteen thousand, nine hundred ninety".