21266521 has 2 divisors, whose sum is σ = 21266522. Its totient is φ = 21266520.

The previous prime is 21266519. The next prime is 21266551. The reversal of 21266521 is 12566212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15210000 + 6056521 = 3900^2 + 2461^2 .

It is a cyclic number.

It is not a de Polignac number, because 21266521 - 2¹ = 21266519 is a prime.

Together with 21266519, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21266551) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10633260 + 10633261.

It is an arithmetic number, because the mean of its divisors is an integer number (10633261).

Almost surely, 2^21266521 is an apocalyptic number.

It is an amenable number.

21266521 is a deficient number, since it is larger than the sum of its proper divisors (1).

21266521 is an equidigital number, since it uses as much as digits as its factorization.

21266521 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1440, while the sum is 25.

The square root of 21266521 is about 4611.5638345360. The cubic root of 21266521 is about 277.0546751800.

The spelling of 21266521 in words is "twenty-one million, two hundred sixty-six thousand, five hundred twenty-one".