21817937 has 2 divisors, whose sum is σ = 21817938. Its totient is φ = 21817936.

The previous prime is 21817907. The next prime is 21817951. The reversal of 21817937 is 73971812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 18011536 + 3806401 = 4244^2 + 1951^2 .

It is a cyclic number.

It is not a de Polignac number, because 21817937 - 2¹⁴ = 21801553 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21817937.

It is not a weakly prime, because it can be changed into another prime (21817907) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10908968 + 10908969.

It is an arithmetic number, because the mean of its divisors is an integer number (10908969).

Almost surely, 2^21817937 is an apocalyptic number.

It is an amenable number.

21817937 is a deficient number, since it is larger than the sum of its proper divisors (1).

21817937 is an equidigital number, since it uses as much as digits as its factorization.

21817937 is an evil number, because the sum of its binary digits is even.

The product of its digits is 21168, while the sum is 38.

The square root of 21817937 is about 4670.9674586749. The cubic root of 21817937 is about 279.4288399589.

The spelling of 21817937 in words is "twenty-one million, eight hundred seventeen thousand, nine hundred thirty-seven".