21018631 has 2 divisors, whose sum is σ = 21018632. Its totient is φ = 21018630.

The previous prime is 21018623. The next prime is 21018659. The reversal of 21018631 is 13681012.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21018631 - 2³ = 21018623 is a prime.

It is a super-2 number, since 2×21018631² = 883565698228322, which contains 22 as substring.

It is a Chen prime.

It is equal to p_1331086 and since 21018631 and 1331086 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21018601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10509315 + 10509316.

It is an arithmetic number, because the mean of its divisors is an integer number (10509316).

Almost surely, 2^21018631 is an apocalyptic number.

21018631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21018631 is an equidigital number, since it uses as much as digits as its factorization.

21018631 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 288, while the sum is 22.

The square root of 21018631 is about 4584.6080530401. The cubic root of 21018631 is about 275.9739832299.

Adding to 21018631 its reverse (13681012), we get a palindrome (34699643).

The spelling of 21018631 in words is "twenty-one million, eighteen thousand, six hundred thirty-one".