21721933 has 2 divisors, whose sum is σ = 21721934. Its totient is φ = 21721932.

The previous prime is 21721927. The next prime is 21721939. The reversal of 21721933 is 33912712.

It is a balanced prime because it is at equal distance from previous prime (21721927) and next prime (21721939).

It can be written as a sum of positive squares in only one way, i.e., 13410244 + 8311689 = 3662^2 + 2883^2 .

It is a cyclic number.

It is not a de Polignac number, because 21721933 - 2⁵ = 21721901 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21721939) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10860966 + 10860967.

It is an arithmetic number, because the mean of its divisors is an integer number (10860967).

Almost surely, 2^21721933 is an apocalyptic number.

It is an amenable number.

21721933 is a deficient number, since it is larger than the sum of its proper divisors (1).

21721933 is an equidigital number, since it uses as much as digits as its factorization.

21721933 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2268, while the sum is 28.

The square root of 21721933 is about 4660.6794569033. The cubic root of 21721933 is about 279.0183866986.

The spelling of 21721933 in words is "twenty-one million, seven hundred twenty-one thousand, nine hundred thirty-three".