21090651 has 4 divisors (see below), whose sum is σ = 28120872. Its totient is φ = 14060432.

The previous prime is 21090647. The next prime is 21090673. The reversal of 21090651 is 15609012.

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 21090651 - 2² = 21090647 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21090631) 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, 3515106 + ... + 3515111.

It is an arithmetic number, because the mean of its divisors is an integer number (7030218).

Almost surely, 2^21090651 is an apocalyptic number.

21090651 is a deficient number, since it is larger than the sum of its proper divisors (7030221).

21090651 is an equidigital number, since it uses as much as digits as its factorization.

21090651 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 7030220.

The product of its (nonzero) digits is 540, while the sum is 24.

The square root of 21090651 is about 4592.4558789388. The cubic root of 21090651 is about 276.2888306970.

Adding to 21090651 its reverse (15609012), we get a palindrome (36699663).

The spelling of 21090651 in words is "twenty-one million, ninety thousand, six hundred fifty-one".