21386857 has 2 divisors, whose sum is σ = 21386858. Its totient is φ = 21386856.

The previous prime is 21386821. The next prime is 21386861. The reversal of 21386857 is 75868312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15452761 + 5934096 = 3931^2 + 2436^2 .

It is a cyclic number.

It is not a de Polignac number, because 21386857 - 2¹¹ = 21384809 is a prime.

It is not a weakly prime, because it can be changed into another prime (21386257) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10693428 + 10693429.

It is an arithmetic number, because the mean of its divisors is an integer number (10693429).

Almost surely, 2^21386857 is an apocalyptic number.

It is an amenable number.

21386857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21386857 is an equidigital number, since it uses as much as digits as its factorization.

21386857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 80640, while the sum is 40.

The square root of 21386857 is about 4624.5926307081. The cubic root of 21386857 is about 277.5762612685.

The spelling of 21386857 in words is "twenty-one million, three hundred eighty-six thousand, eight hundred fifty-seven".