21490 has 16 divisors (see below), whose sum is σ = 44352. Its totient is φ = 7344.

The previous prime is 21487. The next prime is 21491. The reversal of 21490 is 9412.

21490 = T₃₆ + T₃₇ + ... + T₅₅.

21490 = 13² + 14² + ... + 40².

It is an alternating number because its digits alternate between even and odd.

It is not an unprimeable number, because it can be changed into a prime (21491) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 84 + ... + 223.

It is an arithmetic number, because the mean of its divisors is an integer number (2772).

2²¹⁴⁹⁰ is an apocalyptic number.

21490 is an abundant number, since it is smaller than the sum of its proper divisors (22862).

It is a weird number, because it is abundant, but not a pseudoperfect number.

It is a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (22176).

21490 is a wasteful number, since it uses less digits than its factorization.

21490 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 321.

The product of its (nonzero) digits is 72, while the sum is 16.

The square root of 21490 is about 146.5946793032. The cubic root of 21490 is about 27.8021770805.

The spelling of 21490 in words is "twenty-one thousand, four hundred ninety".