21409857 has 12 divisors (see below), whose sum is σ = 35343360. Its totient is φ = 12234168.

The previous prime is 21409847. The next prime is 21409867. The reversal of 21409857 is 75890412.

It is an interprime number because it is at equal distance from previous prime (21409847) and next prime (21409867).

It is not a de Polignac number, because 21409857 - 2⁶ = 21409793 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21409807) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 169857 + ... + 169982.

It is an arithmetic number, because the mean of its divisors is an integer number (2945280).

Almost surely, 2^21409857 is an apocalyptic number.

It is an amenable number.

21409857 is a deficient number, since it is larger than the sum of its proper divisors (13933503).

21409857 is a wasteful number, since it uses less digits than its factorization.

21409857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 339852 (or 339849 counting only the distinct ones).

The product of its (nonzero) digits is 20160, while the sum is 36.

The square root of 21409857 is about 4627.0786680151. The cubic root of 21409857 is about 277.6757299402.

The spelling of 21409857 in words is "twenty-one million, four hundred nine thousand, eight hundred fifty-seven".