21157243 has 2 divisors, whose sum is σ = 21157244. Its totient is φ = 21157242.

The previous prime is 21157207. The next prime is 21157249. The reversal of 21157243 is 34275112.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21157243 - 2¹⁷ = 21026171 is a prime.

It is a super-2 number, since 2×21157243² = 895257862722098, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21157249) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10578621 + 10578622.

It is an arithmetic number, because the mean of its divisors is an integer number (10578622).

Almost surely, 2^21157243 is an apocalyptic number.

21157243 is a deficient number, since it is larger than the sum of its proper divisors (1).

21157243 is an equidigital number, since it uses as much as digits as its factorization.

21157243 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1680, while the sum is 25.

The square root of 21157243 is about 4599.7003163250. The cubic root of 21157243 is about 276.5793116255.

The spelling of 21157243 in words is "twenty-one million, one hundred fifty-seven thousand, two hundred forty-three".