21006731 has 2 divisors, whose sum is σ = 21006732. Its totient is φ = 21006730.

The previous prime is 21006707. The next prime is 21006737. The reversal of 21006731 is 13760012.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21006731 - 2¹⁰ = 21005707 is a prime.

It is a super-2 number, since 2×21006731² = 882565494612722, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21006737) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10503365 + 10503366.

It is an arithmetic number, because the mean of its divisors is an integer number (10503366).

Almost surely, 2^21006731 is an apocalyptic number.

21006731 is a deficient number, since it is larger than the sum of its proper divisors (1).

21006731 is an equidigital number, since it uses as much as digits as its factorization.

21006731 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 252, while the sum is 20.

The square root of 21006731 is about 4583.3100484257. The cubic root of 21006731 is about 275.9218911856.

Adding to 21006731 its reverse (13760012), we get a palindrome (34766743).

The spelling of 21006731 in words is "twenty-one million, six thousand, seven hundred thirty-one".