21782731 has 2 divisors, whose sum is σ = 21782732. Its totient is φ = 21782730.

The previous prime is 21782723. The next prime is 21782737. The reversal of 21782731 is 13728712.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21782731 - 2³ = 21782723 is a prime.

It is a super-2 number, since 2×21782731² = 948974739636722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21782693 and 21782702.

It is not a weakly prime, because it can be changed into another prime (21782737) 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, 10891365 + 10891366.

It is an arithmetic number, because the mean of its divisors is an integer number (10891366).

Almost surely, 2^21782731 is an apocalyptic number.

21782731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21782731 is an equidigital number, since it uses as much as digits as its factorization.

21782731 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4704, while the sum is 31.

The square root of 21782731 is about 4667.1973388748. The cubic root of 21782731 is about 279.2784611234.

The spelling of 21782731 in words is "twenty-one million, seven hundred eighty-two thousand, seven hundred thirty-one".