21537869 has 2 divisors, whose sum is σ = 21537870. Its totient is φ = 21537868.

The previous prime is 21537863. The next prime is 21537871. The reversal of 21537869 is 96873512.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21501769 + 36100 = 4637^2 + 190^2 .

It is a cyclic number.

It is not a de Polignac number, because 21537869 - 2⁸ = 21537613 is a prime.

It is a super-2 number, since 2×21537869² = 927759602122322, which contains 22 as substring.

Together with 21537871, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21537863) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10768934 + 10768935.

It is an arithmetic number, because the mean of its divisors is an integer number (10768935).

Almost surely, 2^21537869 is an apocalyptic number.

It is an amenable number.

21537869 is a deficient number, since it is larger than the sum of its proper divisors (1).

21537869 is an equidigital number, since it uses as much as digits as its factorization.

21537869 is an evil number, because the sum of its binary digits is even.

The product of its digits is 90720, while the sum is 41.

The square root of 21537869 is about 4640.8909704926. The cubic root of 21537869 is about 278.2280489918.

The spelling of 21537869 in words is "twenty-one million, five hundred thirty-seven thousand, eight hundred sixty-nine".