21690961 has 2 divisors, whose sum is σ = 21690962. Its totient is φ = 21690960.

The previous prime is 21690959. The next prime is 21690967. The reversal of 21690961 is 16909612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11730625 + 9960336 = 3425^2 + 3156^2 .

It is a cyclic number.

It is not a de Polignac number, because 21690961 - 2¹ = 21690959 is a prime.

Together with 21690959, it forms a pair of twin primes.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (21690967) 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, 10845480 + 10845481.

It is an arithmetic number, because the mean of its divisors is an integer number (10845481).

Almost surely, 2^21690961 is an apocalyptic number.

It is an amenable number.

21690961 is a deficient number, since it is larger than the sum of its proper divisors (1).

21690961 is an equidigital number, since it uses as much as digits as its factorization.

21690961 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5832, while the sum is 34.

The square root of 21690961 is about 4657.3555801549. The cubic root of 21690961 is about 278.8857117661.

The spelling of 21690961 in words is "twenty-one million, six hundred ninety thousand, nine hundred sixty-one".