21930721 has 2 divisors, whose sum is σ = 21930722. Its totient is φ = 21930720.

The previous prime is 21930709. The next prime is 21930737. The reversal of 21930721 is 12703912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19713600 + 2217121 = 4440^2 + 1489^2 .

It is a cyclic number.

It is not a de Polignac number, because 21930721 - 2¹³ = 21922529 is a prime.

It is not a weakly prime, because it can be changed into another prime (21930791) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10965360 + 10965361.

It is an arithmetic number, because the mean of its divisors is an integer number (10965361).

Almost surely, 2^21930721 is an apocalyptic number.

It is an amenable number.

21930721 is a deficient number, since it is larger than the sum of its proper divisors (1).

21930721 is an equidigital number, since it uses as much as digits as its factorization.

21930721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 21930721 is about 4683.0247703808. The cubic root of 21930721 is about 279.9094988127.

The spelling of 21930721 in words is "twenty-one million, nine hundred thirty thousand, seven hundred twenty-one".