21670821 has 10 divisors (see below), whose sum is σ = 32372582. Its totient is φ = 14447160.

The previous prime is 21670819. The next prime is 21670861. The reversal of 21670821 is 12807612.

It can be written as a sum of positive squares in only one way, i.e., 16769025 + 4901796 = 4095^2 + 2214^2 .

It is not a de Polignac number, because 21670821 - 2¹ = 21670819 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21670861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 133690 + ... + 133851.

Almost surely, 2^21670821 is an apocalyptic number.

It is an amenable number.

21670821 is a deficient number, since it is larger than the sum of its proper divisors (10701761).

21670821 is an equidigital number, since it uses as much as digits as its factorization.

21670821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 267553 (or 267544 counting only the distinct ones).

The product of its (nonzero) digits is 1344, while the sum is 27.

The square root of 21670821 is about 4655.1929068514. The cubic root of 21670821 is about 278.7993701557.

The spelling of 21670821 in words is "twenty-one million, six hundred seventy thousand, eight hundred twenty-one".