21716861 has 2 divisors, whose sum is σ = 21716862. Its totient is φ = 21716860.

The previous prime is 21716857. The next prime is 21716869. The reversal of 21716861 is 16861712.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 12602500 + 9114361 = 3550^2 + 3019^2 .

It is a cyclic number.

It is not a de Polignac number, because 21716861 - 2² = 21716857 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21716869) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10858430 + 10858431.

It is an arithmetic number, because the mean of its divisors is an integer number (10858431).

Almost surely, 2^21716861 is an apocalyptic number.

It is an amenable number.

21716861 is a deficient number, since it is larger than the sum of its proper divisors (1).

21716861 is an equidigital number, since it uses as much as digits as its factorization.

21716861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4032, while the sum is 32.

The square root of 21716861 is about 4660.1352984651. The cubic root of 21716861 is about 278.9966683826.

The spelling of 21716861 in words is "twenty-one million, seven hundred sixteen thousand, eight hundred sixty-one".