21665917837 has 2 divisors, whose sum is σ = 21665917838. Its totient is φ = 21665917836.

The previous prime is 21665917817. The next prime is 21665917843. The reversal of 21665917837 is 73871956612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21579316201 + 86601636 = 146899^2 + 9306^2 .

It is a cyclic number.

It is not a de Polignac number, because 21665917837 - 2³¹ = 19518434189 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21665917807) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10832958918 + 10832958919.

It is an arithmetic number, because the mean of its divisors is an integer number (10832958919).

Almost surely, 2^21665917837 is an apocalyptic number.

It is an amenable number.

21665917837 is a deficient number, since it is larger than the sum of its proper divisors (1).

21665917837 is an equidigital number, since it uses as much as digits as its factorization.

21665917837 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3810240, while the sum is 55.

The spelling of 21665917837 in words is "twenty-one billion, six hundred sixty-five million, nine hundred seventeen thousand, eight hundred thirty-seven".