21166521 has 8 divisors (see below), whose sum is σ = 29132544. Its totient is φ = 13655760.

The previous prime is 21166517. The next prime is 21166529. The reversal of 21166521 is 12566112.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21166521 - 2² = 21166517 is a prime.

It is a super-2 number, since 2×21166521² = 896043222486882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21166491 and 21166500.

It is not an unprimeable number, because it can be changed into a prime (21166529) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 113706 + ... + 113891.

It is an arithmetic number, because the mean of its divisors is an integer number (3641568).

Almost surely, 2^21166521 is an apocalyptic number.

It is an amenable number.

21166521 is a deficient number, since it is larger than the sum of its proper divisors (7966023).

21166521 is a wasteful number, since it uses less digits than its factorization.

21166521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 227631.

The product of its digits is 720, while the sum is 24.

The square root of 21166521 is about 4600.7087497472. The cubic root of 21166521 is about 276.6197347853.

It can be divided in two parts, 2116652 and 1, that added together give a triangular number (2116653 = T₂₀₅₇).

The spelling of 21166521 in words is "twenty-one million, one hundred sixty-six thousand, five hundred twenty-one".