21531739 has 2 divisors, whose sum is σ = 21531740. Its totient is φ = 21531738.

The previous prime is 21531737. The next prime is 21531773. The reversal of 21531739 is 93713512.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21531739 - 2¹ = 21531737 is a prime.

Together with 21531737, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 21531739.

It is not a weakly prime, because it can be changed into another prime (21531733) 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, 10765869 + 10765870.

It is an arithmetic number, because the mean of its divisors is an integer number (10765870).

Almost surely, 2^21531739 is an apocalyptic number.

21531739 is a deficient number, since it is larger than the sum of its proper divisors (1).

21531739 is an equidigital number, since it uses as much as digits as its factorization.

21531739 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 5670, while the sum is 31.

The square root of 21531739 is about 4640.2304899649. The cubic root of 21531739 is about 278.2016505310.

The spelling of 21531739 in words is "twenty-one million, five hundred thirty-one thousand, seven hundred thirty-nine".