21721784 has 32 divisors (see below), whose sum is σ = 49286880. Its totient is φ = 8761344.

The previous prime is 21721781. The next prime is 21721787. The reversal of 21721784 is 48712712.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21721781) and next prime (21721787).

It is a nude number because it is divisible by every one of its digits.

It is a self number, because there is not a number n which added to its sum of digits gives 21721784.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21721781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10457 + ... + 12360.

It is an arithmetic number, because the mean of its divisors is an integer number (1540215).

Almost surely, 2^21721784 is an apocalyptic number.

It is an amenable number.

21721784 is an abundant number, since it is smaller than the sum of its proper divisors (27565096).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21721784 is a wasteful number, since it uses less digits than its factorization.

21721784 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 22847 (or 22843 counting only the distinct ones).

The product of its digits is 6272, while the sum is 32.

The square root of 21721784 is about 4660.6634720821. The cubic root of 21721784 is about 279.0177487285.

The spelling of 21721784 in words is "twenty-one million, seven hundred twenty-one thousand, seven hundred eighty-four".