21780971 has 4 divisors (see below), whose sum is σ = 22150200. Its totient is φ = 21411744.

The previous prime is 21780959. The next prime is 21780989. The reversal of 21780971 is 17908712.

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

It is a cyclic number.

It is not a de Polignac number, because 21780971 - 2⁶ = 21780907 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21780991) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 184526 + ... + 184643.

It is an arithmetic number, because the mean of its divisors is an integer number (5537550).

Almost surely, 2^21780971 is an apocalyptic number.

21780971 is a deficient number, since it is larger than the sum of its proper divisors (369229).

21780971 is an equidigital number, since it uses as much as digits as its factorization.

21780971 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369228.

The product of its (nonzero) digits is 7056, while the sum is 35.

The square root of 21780971 is about 4667.0087850785. The cubic root of 21780971 is about 279.2709392118.

The spelling of 21780971 in words is "twenty-one million, seven hundred eighty thousand, nine hundred seventy-one".