21690631 has 2 divisors, whose sum is σ = 21690632. Its totient is φ = 21690630.

The previous prime is 21690629. The next prime is 21690653. The reversal of 21690631 is 13609612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21690631 - 2¹ = 21690629 is a prime.

It is a super-2 number, since 2×21690631² = 940966946356322, which contains 22 as substring.

Together with 21690629, it forms a pair of twin primes.

It is equal to p_1370881 and since 21690631 and 1370881 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21690631.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21690611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845315 + 10845316.

It is an arithmetic number, because the mean of its divisors is an integer number (10845316).

Almost surely, 2^21690631 is an apocalyptic number.

21690631 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690631 is an equidigital number, since it uses as much as digits as its factorization.

21690631 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1944, while the sum is 28.

The square root of 21690631 is about 4657.3201521905. The cubic root of 21690631 is about 278.8842974635.

The spelling of 21690631 in words is "twenty-one million, six hundred ninety thousand, six hundred thirty-one".