21259891 has 2 divisors, whose sum is σ = 21259892. Its totient is φ = 21259890.

The previous prime is 21259873. The next prime is 21259897. The reversal of 21259891 is 19895212.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21259891 - 2¹¹ = 21257843 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21259891.

It is not a weakly prime, because it can be changed into another prime (21259897) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10629945 + 10629946.

It is an arithmetic number, because the mean of its divisors is an integer number (10629946).

Almost surely, 2^21259891 is an apocalyptic number.

21259891 is a deficient number, since it is larger than the sum of its proper divisors (1).

21259891 is an equidigital number, since it uses as much as digits as its factorization.

21259891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12960, while the sum is 37.

The square root of 21259891 is about 4610.8449334151. The cubic root of 21259891 is about 277.0258808854.

The spelling of 21259891 in words is "twenty-one million, two hundred fifty-nine thousand, eight hundred ninety-one".