21879917 has 2 divisors, whose sum is σ = 21879918. Its totient is φ = 21879916.

The previous prime is 21879899. The next prime is 21879929. The reversal of 21879917 is 71997812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20921476 + 958441 = 4574^2 + 979^2 .

It is a cyclic number.

It is not a de Polignac number, because 21879917 - 2⁸ = 21879661 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 (21879947) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10939958 + 10939959.

It is an arithmetic number, because the mean of its divisors is an integer number (10939959).

Almost surely, 2^21879917 is an apocalyptic number.

It is an amenable number.

21879917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21879917 is an equidigital number, since it uses as much as digits as its factorization.

21879917 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 63504, while the sum is 44.

The square root of 21879917 is about 4677.5973533428. The cubic root of 21879917 is about 279.6931885925.

The spelling of 21879917 in words is "twenty-one million, eight hundred seventy-nine thousand, nine hundred seventeen".