21780651 has 4 divisors (see below), whose sum is σ = 29040872. Its totient is φ = 14520432.

The previous prime is 21780623. The next prime is 21780659. The reversal of 21780651 is 15608712.

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

It is not a de Polignac number, because 21780651 - 2⁷ = 21780523 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21780659) 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, 3630106 + ... + 3630111.

It is an arithmetic number, because the mean of its divisors is an integer number (7260218).

Almost surely, 2^21780651 is an apocalyptic number.

21780651 is a deficient number, since it is larger than the sum of its proper divisors (7260221).

21780651 is an equidigital number, since it uses as much as digits as its factorization.

21780651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7260220.

The product of its (nonzero) digits is 3360, while the sum is 30.

The square root of 21780651 is about 4666.9745017516. The cubic root of 21780651 is about 279.2695715480.

The spelling of 21780651 in words is "twenty-one million, seven hundred eighty thousand, six hundred fifty-one".