21921869 has 2 divisors, whose sum is σ = 21921870. Its totient is φ = 21921868.

The previous prime is 21921847. The next prime is 21921899. The reversal of 21921869 is 96812912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11764900 + 10156969 = 3430^2 + 3187^2 .

It is a cyclic number.

It is not a de Polignac number, because 21921869 - 2²⁴ = 5144653 is a prime.

It is a super-2 number, since 2×21921869² = 961136680906322, which contains 22 as substring.

It is a Sophie Germain prime.

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 (21921899) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10960934 + 10960935.

It is an arithmetic number, because the mean of its divisors is an integer number (10960935).

Almost surely, 2^21921869 is an apocalyptic number.

It is an amenable number.

21921869 is a deficient number, since it is larger than the sum of its proper divisors (1).

21921869 is an equidigital number, since it uses as much as digits as its factorization.

21921869 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15552, while the sum is 38.

The square root of 21921869 is about 4682.0795593411. The cubic root of 21921869 is about 279.8718333490.

The spelling of 21921869 in words is "twenty-one million, nine hundred twenty-one thousand, eight hundred sixty-nine".