21372961 has 4 divisors (see below), whose sum is σ = 22630212. Its totient is φ = 20115712.

The previous prime is 21372937. The next prime is 21372977. The reversal of 21372961 is 16927312.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 17272336 + 4100625 = 4156^2 + 2025^2 .

It is a cyclic number.

It is not a de Polignac number, because 21372961 - 2¹¹ = 21370913 is a prime.

It is a Smith number, since the sum of its digits (31) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21372991) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 628600 + ... + 628633.

It is an arithmetic number, because the mean of its divisors is an integer number (5657553).

Almost surely, 2^21372961 is an apocalyptic number.

It is an amenable number.

21372961 is a deficient number, since it is larger than the sum of its proper divisors (1257251).

21372961 is a wasteful number, since it uses less digits than its factorization.

21372961 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1257250.

The product of its digits is 4536, while the sum is 31.

The square root of 21372961 is about 4623.0899839826. The cubic root of 21372961 is about 277.5161303288.

The spelling of 21372961 in words is "twenty-one million, three hundred seventy-two thousand, nine hundred sixty-one".