21216737 has 2 divisors, whose sum is σ = 21216738. Its totient is φ = 21216736.

The previous prime is 21216707. The next prime is 21216739. The reversal of 21216737 is 73761212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18627856 + 2588881 = 4316^2 + 1609^2 .

It is a cyclic number.

It is not a de Polignac number, because 21216737 - 2¹² = 21212641 is a prime.

Together with 21216739, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21216739) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10608368 + 10608369.

It is an arithmetic number, because the mean of its divisors is an integer number (10608369).

Almost surely, 2^21216737 is an apocalyptic number.

It is an amenable number.

21216737 is a deficient number, since it is larger than the sum of its proper divisors (1).

21216737 is an equidigital number, since it uses as much as digits as its factorization.

21216737 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3528, while the sum is 29.

The square root of 21216737 is about 4606.1629367620. The cubic root of 21216737 is about 276.8383152840.

Adding to 21216737 its reverse (73761212), we get a palindrome (94977949).

The spelling of 21216737 in words is "twenty-one million, two hundred sixteen thousand, seven hundred thirty-seven".