21215137 has 2 divisors, whose sum is σ = 21215138. Its totient is φ = 21215136.

The previous prime is 21215111. The next prime is 21215141. The reversal of 21215137 is 73151212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 14371681 + 6843456 = 3791^2 + 2616^2 .

It is a cyclic number.

It is not a de Polignac number, because 21215137 - 2⁷ = 21215009 is a prime.

It is not a weakly prime, because it can be changed into another prime (21215107) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10607568 + 10607569.

It is an arithmetic number, because the mean of its divisors is an integer number (10607569).

Almost surely, 2^21215137 is an apocalyptic number.

It is an amenable number.

21215137 is a deficient number, since it is larger than the sum of its proper divisors (1).

21215137 is an equidigital number, since it uses as much as digits as its factorization.

21215137 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 420, while the sum is 22.

The square root of 21215137 is about 4605.9892531355. The cubic root of 21215137 is about 276.8313561171.

Adding to 21215137 its reverse (73151212), we get a palindrome (94366349).

The spelling of 21215137 in words is "twenty-one million, two hundred fifteen thousand, one hundred thirty-seven".