21685671 has 32 divisors (see below), whose sum is σ = 36979200. Its totient is φ = 12303360.

The previous prime is 21685667. The next prime is 21685687. The reversal of 21685671 is 17658612.

It is not a de Polignac number, because 21685671 - 2² = 21685667 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21685621) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 33511 + ... + 34151.

It is an arithmetic number, because the mean of its divisors is an integer number (1155600).

Almost surely, 2^21685671 is an apocalyptic number.

21685671 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21685671 is a deficient number, since it is larger than the sum of its proper divisors (15293529).

21685671 is a wasteful number, since it uses less digits than its factorization.

21685671 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 836 (or 830 counting only the distinct ones).

The product of its digits is 20160, while the sum is 36.

The square root of 21685671 is about 4656.7876266800. The cubic root of 21685671 is about 278.8630383376.

The spelling of 21685671 in words is "twenty-one million, six hundred eighty-five thousand, six hundred seventy-one".