21690629 has 2 divisors, whose sum is σ = 21690630. Its totient is φ = 21690628.

The previous prime is 21690611. The next prime is 21690631. The reversal of 21690629 is 92609612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 11546404 + 10144225 = 3398^2 + 3185^2 .

It is a cyclic number.

It is not a de Polignac number, because 21690629 - 2²⁰ = 20642053 is a prime.

It is a Sophie Germain prime.

Together with 21690631, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21690329) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10845314 + 10845315.

It is an arithmetic number, because the mean of its divisors is an integer number (10845315).

Almost surely, 2^21690629 is an apocalyptic number.

It is an amenable number.

21690629 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690629 is an equidigital number, since it uses as much as digits as its factorization.

21690629 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11664, while the sum is 35.

The square root of 21690629 is about 4657.3199374748. The cubic root of 21690629 is about 278.8842888919.

The spelling of 21690629 in words is "twenty-one million, six hundred ninety thousand, six hundred twenty-nine".