21685881 has 24 divisors (see below), whose sum is σ = 34801920. Its totient is φ = 11962272.

The previous prime is 21685879. The next prime is 21685913. The reversal of 21685881 is 18858612.

It is not a de Polignac number, because 21685881 - 2¹ = 21685879 is a prime.

It is a super-2 number, since 2×21685881² = 940554869492322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21685801) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 1720 + ... + 6806.

It is an arithmetic number, because the mean of its divisors is an integer number (1450080).

Almost surely, 2^21685881 is an apocalyptic number.

21685881 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

It is an amenable number.

21685881 is a deficient number, since it is larger than the sum of its proper divisors (13116039).

21685881 is a wasteful number, since it uses less digits than its factorization.

21685881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5133 (or 5126 counting only the distinct ones).

The product of its digits is 30720, while the sum is 39.

The square root of 21685881 is about 4656.8101743576. The cubic root of 21685881 is about 278.8639384873.

The spelling of 21685881 in words is "twenty-one million, six hundred eighty-five thousand, eight hundred eighty-one".