21916021 has 2 divisors, whose sum is σ = 21916022. Its totient is φ = 21916020.

The previous prime is 21916003. The next prime is 21916051. The reversal of 21916021 is 12061912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21298225 + 617796 = 4615^2 + 786^2 .

It is a cyclic number.

It is not a de Polignac number, because 21916021 - 2⁷ = 21915893 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21915983 and 21916001.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21916001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10958010 + 10958011.

It is an arithmetic number, because the mean of its divisors is an integer number (10958011).

Almost surely, 2^21916021 is an apocalyptic number.

It is an amenable number.

21916021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21916021 is an equidigital number, since it uses as much as digits as its factorization.

21916021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 216, while the sum is 22.

The square root of 21916021 is about 4681.4550088621. The cubic root of 21916021 is about 279.8469444121.

Adding to 21916021 its reverse (12061912), we get a palindrome (33977933).

The spelling of 21916021 in words is "twenty-one million, nine hundred sixteen thousand, twenty-one".