21901890 has 32 divisors (see below), whose sum is σ = 52975296. Its totient is φ = 5794880.

The previous prime is 21901853. The next prime is 21901897. The reversal of 21901890 is 9810912.

It is a Harshad number since it is a multiple of its sum of digits (30).

It is not an unprimeable number, because it can be changed into a prime (21901897) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1144 + ... + 6716.

It is an arithmetic number, because the mean of its divisors is an integer number (1655478).

Almost surely, 2^21901890 is an apocalyptic number.

21901890 is an abundant number, since it is smaller than the sum of its proper divisors (31073406).

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

21901890 is a wasteful number, since it uses less digits than its factorization.

21901890 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5714.

The product of its (nonzero) digits is 1296, while the sum is 30.

The square root of 21901890 is about 4679.9455125033. The cubic root of 21901890 is about 279.7867849606.

It can be divided in two parts, 21901 and 890, that added together give a triangular number (22791 = T₂₁₃).

The spelling of 21901890 in words is "twenty-one million, nine hundred one thousand, eight hundred ninety".