21243731 has 2 divisors, whose sum is σ = 21243732. Its totient is φ = 21243730.

The previous prime is 21243721. The next prime is 21243769. The reversal of 21243731 is 13734212.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21243731 is a prime.

It is a super-2 number, since 2×21243731² = 902592213600722, which contains 22 as substring.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21243697 and 21243706.

It is not a weakly prime, because it can be changed into another prime (21243721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10621865 + 10621866.

It is an arithmetic number, because the mean of its divisors is an integer number (10621866).

Almost surely, 2^21243731 is an apocalyptic number.

21243731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21243731 is an equidigital number, since it uses as much as digits as its factorization.

21243731 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1008, while the sum is 23.

The square root of 21243731 is about 4609.0922099693. The cubic root of 21243731 is about 276.9556724195.

Adding to 21243731 its reverse (13734212), we get a palindrome (34977943).

The spelling of 21243731 in words is "twenty-one million, two hundred forty-three thousand, seven hundred thirty-one".