21170857 has 2 divisors, whose sum is σ = 21170858. Its totient is φ = 21170856.

The previous prime is 21170789. The next prime is 21170881. The reversal of 21170857 is 75807112.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17799961 + 3370896 = 4219^2 + 1836^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21170857 is a prime.

It is a super-2 number, since 2×21170857² = 896410372228898, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21170887) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10585428 + 10585429.

It is an arithmetic number, because the mean of its divisors is an integer number (10585429).

Almost surely, 2^21170857 is an apocalyptic number.

It is an amenable number.

21170857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21170857 is an equidigital number, since it uses as much as digits as its factorization.

21170857 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3920, while the sum is 31.

The square root of 21170857 is about 4601.1799573588. The cubic root of 21170857 is about 276.6386221795.

Adding to 21170857 its reverse (75807112), we get a palindrome (96977969).

The spelling of 21170857 in words is "twenty-one million, one hundred seventy thousand, eight hundred fifty-seven".