21661750 has 32 divisors (see below), whose sum is σ = 44242848. Its totient is φ = 7876000.

The previous prime is 21661733. The next prime is 21661781. The reversal of 21661750 is 5716612.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1189 + ... + 6688.

It is an arithmetic number, because the mean of its divisors is an integer number (1382589).

Almost surely, 2^21661750 is an apocalyptic number.

21661750 is an abundant number, since it is smaller than the sum of its proper divisors (22581098).

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

21661750 is a wasteful number, since it uses less digits than its factorization.

21661750 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7905 (or 7895 counting only the distinct ones).

The product of its (nonzero) digits is 2520, while the sum is 28.

The square root of 21661750 is about 4654.2185165718. The cubic root of 21661750 is about 278.7604646611.

It can be divided in two parts, 2166 and 1750, that added together give a triangular number (3916 = T₈₈).

The spelling of 21661750 in words is "twenty-one million, six hundred sixty-one thousand, seven hundred fifty".