21645901 has 2 divisors, whose sum is σ = 21645902. Its totient is φ = 21645900.

The previous prime is 21645881. The next prime is 21645907. The reversal of 21645901 is 10954612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19758025 + 1887876 = 4445^2 + 1374^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21645901 is a prime.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21645901.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21645907) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10822950 + 10822951.

It is an arithmetic number, because the mean of its divisors is an integer number (10822951).

Almost surely, 2^21645901 is an apocalyptic number.

It is an amenable number.

21645901 is a deficient number, since it is larger than the sum of its proper divisors (1).

21645901 is an equidigital number, since it uses as much as digits as its factorization.

21645901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2160, while the sum is 28.

The square root of 21645901 is about 4652.5155561266. The cubic root of 21645901 is about 278.6924622674.

The spelling of 21645901 in words is "twenty-one million, six hundred forty-five thousand, nine hundred one".