21078857 has 2 divisors, whose sum is σ = 21078858. Its totient is φ = 21078856.

The previous prime is 21078851. The next prime is 21078877. The reversal of 21078857 is 75887012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15178816 + 5900041 = 3896^2 + 2429^2 .

It is a cyclic number.

It is not a de Polignac number, because 21078857 - 2⁸ = 21078601 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 21078857.

It is not a weakly prime, because it can be changed into another prime (21078851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10539428 + 10539429.

It is an arithmetic number, because the mean of its divisors is an integer number (10539429).

Almost surely, 2^21078857 is an apocalyptic number.

It is an amenable number.

21078857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21078857 is an equidigital number, since it uses as much as digits as its factorization.

21078857 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 31360, while the sum is 38.

The square root of 21078857 is about 4591.1716369572. The cubic root of 21078857 is about 276.2373203847.

The spelling of 21078857 in words is "twenty-one million, seventy-eight thousand, eight hundred fifty-seven".