21681837 has 10 divisors (see below), whose sum is σ = 32389038. Its totient is φ = 14454504.

The previous prime is 21681833. The next prime is 21681839. The reversal of 21681837 is 73818612.

It can be written as a sum of positive squares in only one way, i.e., 21399876 + 281961 = 4626^2 + 531^2 .

It is not a de Polignac number, because 21681837 - 2² = 21681833 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21681833) by changing a digit.

It is a polite number, since it can be written in 9 ways as a sum of consecutive naturals, for example, 133758 + ... + 133919.

Almost surely, 2^21681837 is an apocalyptic number.

21681837 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21681837 is a deficient number, since it is larger than the sum of its proper divisors (10707201).

21681837 is an equidigital number, since it uses as much as digits as its factorization.

21681837 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 267689 (or 267680 counting only the distinct ones).

The product of its digits is 16128, while the sum is 36.

The square root of 21681837 is about 4656.3759513166. The cubic root of 21681837 is about 278.8466031547.

It can be divided in two parts, 2168 and 1837, that added together give a triangular number (4005 = T₈₉).

The spelling of 21681837 in words is "twenty-one million, six hundred eighty-one thousand, eight hundred thirty-seven".