21662021 has 6 divisors (see below), whose sum is σ = 22645350. Its totient is φ = 20719688.

The previous prime is 21661999. The next prime is 21662041. The reversal of 21662021 is 12026612.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 18105025 + 3556996 = 4255^2 + 1886^2 .

It is a de Polignac number, because none of the positive numbers 2^k-21662021 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21661984 and 21662002.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21662041) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 19946 + ... + 21003.

It is an arithmetic number, because the mean of its divisors is an integer number (3774225).

Almost surely, 2^21662021 is an apocalyptic number.

It is an amenable number.

21662021 is a deficient number, since it is larger than the sum of its proper divisors (983329).

21662021 is an equidigital number, since it uses as much as digits as its factorization.

21662021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 40995 (or 40972 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 21662021 is about 4654.2476298538. The cubic root of 21662021 is about 278.7616271367.

Adding to 21662021 its reverse (12026612), we get a palindrome (33688633).

The spelling of 21662021 in words is "twenty-one million, six hundred sixty-two thousand, twenty-one".