21406890 has 16 divisors (see below), whose sum is σ = 51376608. Its totient is φ = 5708496.

The previous prime is 21406883. The next prime is 21406897. The reversal of 21406890 is 9860412.

It is an interprime number because it is at equal distance from previous prime (21406883) and next prime (21406897).

It is a Harshad number since it is a multiple of its sum of digits (30), and also a Moran number because the ratio is a prime number: 713563 = 21406890 / (2 + 1 + 4 + 0 + 6 + 8 + 9 + 0).

It is not an unprimeable number, because it can be changed into a prime (21406897) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 356752 + ... + 356811.

It is an arithmetic number, because the mean of its divisors is an integer number (3211038).

Almost surely, 2^21406890 is an apocalyptic number.

21406890 is an abundant number, since it is smaller than the sum of its proper divisors (29969718).

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

21406890 is a wasteful number, since it uses less digits than its factorization.

21406890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 713573.

The product of its (nonzero) digits is 3456, while the sum is 30.

The square root of 21406890 is about 4626.7580442465. The cubic root of 21406890 is about 277.6629024849.

The spelling of 21406890 in words is "twenty-one million, four hundred six thousand, eight hundred ninety".