21721747 has 2 divisors, whose sum is σ = 21721748. Its totient is φ = 21721746.

The previous prime is 21721741. The next prime is 21721781. The reversal of 21721747 is 74712712.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21721747 - 2¹¹ = 21719699 is a prime.

It is not a weakly prime, because it can be changed into another prime (21721741) 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 as a sum of consecutive naturals, namely, 10860873 + 10860874.

It is an arithmetic number, because the mean of its divisors is an integer number (10860874).

Almost surely, 2^21721747 is an apocalyptic number.

21721747 is a deficient number, since it is larger than the sum of its proper divisors (1).

21721747 is an equidigital number, since it uses as much as digits as its factorization.

21721747 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5488, while the sum is 31.

The square root of 21721747 is about 4660.6595026884. The cubic root of 21721747 is about 279.0175903059.

The spelling of 21721747 in words is "twenty-one million, seven hundred twenty-one thousand, seven hundred forty-seven".