21406549 has 2 divisors, whose sum is σ = 21406550. Its totient is φ = 21406548.

The previous prime is 21406543. The next prime is 21406589. The reversal of 21406549 is 94560412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21252100 + 154449 = 4610^2 + 393^2 .

It is a cyclic number.

It is not a de Polignac number, because 21406549 - 2⁹ = 21406037 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21406549.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21406543) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10703274 + 10703275.

It is an arithmetic number, because the mean of its divisors is an integer number (10703275).

Almost surely, 2^21406549 is an apocalyptic number.

It is an amenable number.

21406549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21406549 is an equidigital number, since it uses as much as digits as its factorization.

21406549 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 8640, while the sum is 31.

The square root of 21406549 is about 4626.7211932426. The cubic root of 21406549 is about 277.6614281379.

The spelling of 21406549 in words is "twenty-one million, four hundred six thousand, five hundred forty-nine".