21221001 has 8 divisors (see below), whose sum is σ = 31438560. Its totient is φ = 14147316.

The previous prime is 21220993. The next prime is 21221003. The reversal of 21221001 is 10012212.

It is not a de Polignac number, because 21221001 - 2³ = 21220993 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (9).

It is not an unprimeable number, because it can be changed into a prime (21221003) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 392955 + ... + 393008.

It is an arithmetic number, because the mean of its divisors is an integer number (3929820).

Almost surely, 2^21221001 is an apocalyptic number.

It is an amenable number.

21221001 is a deficient number, since it is larger than the sum of its proper divisors (10217559).

21221001 is an equidigital number, since it uses as much as digits as its factorization.

21221001 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 785972 (or 785966 counting only the distinct ones).

The product of its (nonzero) digits is 8, while the sum is 9.

The square root of 21221001 is about 4606.6257716467. The cubic root of 21221001 is about 276.8568597552.

Adding to 21221001 its reverse (10012212), we get a palindrome (31233213).

The spelling of 21221001 in words is "twenty-one million, two hundred twenty-one thousand, one".