21756651 has 16 divisors (see below), whose sum is σ = 35103744. Its totient is φ = 11700864.

The previous prime is 21756649. The next prime is 21756671. The reversal of 21756651 is 15665712.

It is not a de Polignac number, because 21756651 - 2¹ = 21756649 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21756671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 30115 + ... + 30828.

It is an arithmetic number, because the mean of its divisors is an integer number (2193984).

Almost surely, 2^21756651 is an apocalyptic number.

21756651 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21756651 is a deficient number, since it is larger than the sum of its proper divisors (13347093).

21756651 is a wasteful number, since it uses less digits than its factorization.

21756651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 60970.

The product of its digits is 12600, while the sum is 33.

The square root of 21756651 is about 4664.4025340873. The cubic root of 21756651 is about 279.1669585601.

The spelling of 21756651 in words is "twenty-one million, seven hundred fifty-six thousand, six hundred fifty-one".