21869521 has 2 divisors, whose sum is σ = 21869522. Its totient is φ = 21869520.

The previous prime is 21869483. The next prime is 21869557. The reversal of 21869521 is 12596812.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13395600 + 8473921 = 3660^2 + 2911^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21869521 is a prime.

It is equal to p_1381498 and since 21869521 and 1381498 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (21869321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10934760 + 10934761.

It is an arithmetic number, because the mean of its divisors is an integer number (10934761).

Almost surely, 2^21869521 is an apocalyptic number.

It is an amenable number.

21869521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21869521 is an equidigital number, since it uses as much as digits as its factorization.

21869521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8640, while the sum is 34.

The square root of 21869521 is about 4676.4859670483. The cubic root of 21869521 is about 279.6488838689.

The spelling of 21869521 in words is "twenty-one million, eight hundred sixty-nine thousand, five hundred twenty-one".