21501990 has 64 divisors (see below), whose sum is σ = 58000320. Its totient is φ = 5667840.

The previous prime is 21501967. The next prime is 21502001. The reversal of 21501990 is 9910512.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 25780 + ... + 26600.

It is an arithmetic number, because the mean of its divisors is an integer number (906255).

Almost surely, 2^21501990 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21501990, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29000160).

21501990 is an abundant number, since it is smaller than the sum of its proper divisors (36498330).

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

21501990 is a wasteful number, since it uses less digits than its factorization.

21501990 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 934 (or 928 counting only the distinct ones).

The product of its (nonzero) digits is 810, while the sum is 27.

The square root of 21501990 is about 4637.0238300013. The cubic root of 21501990 is about 278.0734671176.

The spelling of 21501990 in words is "twenty-one million, five hundred one thousand, nine hundred ninety".