21221237 has 2 divisors, whose sum is σ = 21221238. Its totient is φ = 21221236.

The previous prime is 21221171. The next prime is 21221251. The reversal of 21221237 is 73212212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11771761 + 9449476 = 3431^2 + 3074^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21221237 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21221257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610618 + 10610619.

It is an arithmetic number, because the mean of its divisors is an integer number (10610619).

Almost surely, 2^21221237 is an apocalyptic number.

It is an amenable number.

21221237 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221237 is an equidigital number, since it uses as much as digits as its factorization.

21221237 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 336, while the sum is 20.

The square root of 21221237 is about 4606.6513868536. The cubic root of 21221237 is about 276.8578860652.

Adding to 21221237 its reverse (73212212), we get a palindrome (94433449).

The spelling of 21221237 in words is "twenty-one million, two hundred twenty-one thousand, two hundred thirty-seven".