21857431 has 2 divisors, whose sum is σ = 21857432. Its totient is φ = 21857430.

The previous prime is 21857411. The next prime is 21857447. The reversal of 21857431 is 13475812.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21857431 - 2¹⁷ = 21726359 is a prime.

It is a super-2 number, since 2×21857431² = 955494579839522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21857393 and 21857402.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21857411) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10928715 + 10928716.

It is an arithmetic number, because the mean of its divisors is an integer number (10928716).

Almost surely, 2^21857431 is an apocalyptic number.

21857431 is a deficient number, since it is larger than the sum of its proper divisors (1).

21857431 is an equidigital number, since it uses as much as digits as its factorization.

21857431 is an evil number, because the sum of its binary digits is even.

The product of its digits is 6720, while the sum is 31.

The square root of 21857431 is about 4675.1931510901. The cubic root of 21857431 is about 279.5973421483.

The spelling of 21857431 in words is "twenty-one million, eight hundred fifty-seven thousand, four hundred thirty-one".