21881917 has 2 divisors, whose sum is σ = 21881918. Its totient is φ = 21881916.

The previous prime is 21881903. The next prime is 21881927. The reversal of 21881917 is 71918812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21427641 + 454276 = 4629^2 + 674^2 .

It is a cyclic number.

It is not a de Polignac number, because 21881917 - 2⁷ = 21881789 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21881927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10940958 + 10940959.

It is an arithmetic number, because the mean of its divisors is an integer number (10940959).

Almost surely, 2^21881917 is an apocalyptic number.

It is an amenable number.

21881917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21881917 is an equidigital number, since it uses as much as digits as its factorization.

21881917 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8064, while the sum is 37.

The square root of 21881917 is about 4677.8111334255. The cubic root of 21881917 is about 279.7017104002.

The spelling of 21881917 in words is "twenty-one million, eight hundred eighty-one thousand, nine hundred seventeen".