21781873 has 2 divisors, whose sum is σ = 21781874. Its totient is φ = 21781872.

The previous prime is 21781843. The next prime is 21781891. The reversal of 21781873 is 37818712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15745024 + 6036849 = 3968^2 + 2457^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21781873 is a prime.

It is not a weakly prime, because it can be changed into another prime (21781843) 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, 10890936 + 10890937.

It is an arithmetic number, because the mean of its divisors is an integer number (10890937).

Almost surely, 2^21781873 is an apocalyptic number.

It is an amenable number.

21781873 is a deficient number, since it is larger than the sum of its proper divisors (1).

21781873 is an equidigital number, since it uses as much as digits as its factorization.

21781873 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 18816, while the sum is 37.

The square root of 21781873 is about 4667.1054198507. The cubic root of 21781873 is about 279.2747942422.

The spelling of 21781873 in words is "twenty-one million, seven hundred eighty-one thousand, eight hundred seventy-three".