21631691 has 2 divisors, whose sum is σ = 21631692. Its totient is φ = 21631690.

The previous prime is 21631663. The next prime is 21631697. The reversal of 21631691 is 19613612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21631691 - 2⁶ = 21631627 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21631697) 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, 10815845 + 10815846.

It is an arithmetic number, because the mean of its divisors is an integer number (10815846).

Almost surely, 2^21631691 is an apocalyptic number.

21631691 is a deficient number, since it is larger than the sum of its proper divisors (1).

21631691 is an equidigital number, since it uses as much as digits as its factorization.

21631691 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1944, while the sum is 29.

The square root of 21631691 is about 4650.9881745711. The cubic root of 21631691 is about 278.6314640088.

It can be divided in two parts, 21631 and 691, that added together give a palindrome (22322).

The spelling of 21631691 in words is "twenty-one million, six hundred thirty-one thousand, six hundred ninety-one".