21266501 has 4 divisors (see below), whose sum is σ = 21287052. Its totient is φ = 21245952.

The previous prime is 21266471. The next prime is 21266503. The reversal of 21266501 is 10566212.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 19589476 + 1677025 = 4426^2 + 1295^2 .

It is a cyclic number.

It is not a de Polignac number, because 21266501 - 2²² = 17072197 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21266503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 8636 + ... + 10821.

It is an arithmetic number, because the mean of its divisors is an integer number (5321763).

Almost surely, 2^21266501 is an apocalyptic number.

It is an amenable number.

21266501 is a deficient number, since it is larger than the sum of its proper divisors (20551).

21266501 is a wasteful number, since it uses less digits than its factorization.

21266501 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20550.

The product of its (nonzero) digits is 720, while the sum is 23.

The square root of 21266501 is about 4611.5616660737. The cubic root of 21266501 is about 277.0545883284.

The spelling of 21266501 in words is "twenty-one million, two hundred sixty-six thousand, five hundred one".