21406979 has 16 divisors (see below), whose sum is σ = 24213600. Its totient is φ = 18754560.

The previous prime is 21406967. The next prime is 21406999. The reversal of 21406979 is 97960412.

It is not a de Polignac number, because 21406979 - 2⁴ = 21406963 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21406919) 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, 60467 + ... + 60819.

It is an arithmetic number, because the mean of its divisors is an integer number (1513350).

Almost surely, 2^21406979 is an apocalyptic number.

21406979 is a deficient number, since it is larger than the sum of its proper divisors (2806621).

21406979 is a wasteful number, since it uses less digits than its factorization.

21406979 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 550.

The product of its (nonzero) digits is 27216, while the sum is 38.

The square root of 21406979 is about 4626.7676622022. The cubic root of 21406979 is about 277.6632872826.

It can be divided in two parts, 2140 and 6979, that added together give a palindrome (9119).

The spelling of 21406979 in words is "twenty-one million, four hundred six thousand, nine hundred seventy-nine".