21491669 has 2 divisors, whose sum is σ = 21491670. Its totient is φ = 21491668.

The previous prime is 21491663. The next prime is 21491677. The reversal of 21491669 is 96619412.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20566225 + 925444 = 4535^2 + 962^2 .

It is a cyclic number.

It is not a de Polignac number, because 21491669 - 2⁴ = 21491653 is a prime.

It is a super-2 number, since 2×21491669² = 923783672811122, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21491663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10745834 + 10745835.

It is an arithmetic number, because the mean of its divisors is an integer number (10745835).

Almost surely, 2^21491669 is an apocalyptic number.

It is an amenable number.

21491669 is a deficient number, since it is larger than the sum of its proper divisors (1).

21491669 is an equidigital number, since it uses as much as digits as its factorization.

21491669 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 23328, while the sum is 38.

The square root of 21491669 is about 4635.9108058719. The cubic root of 21491669 is about 278.0289680491.

The spelling of 21491669 in words is "twenty-one million, four hundred ninety-one thousand, six hundred sixty-nine".