21706640 has 20 divisors (see below), whose sum is σ = 50468124. Its totient is φ = 8682624.

The previous prime is 21706639. The next prime is 21706693. The reversal of 21706640 is 4660712.

It can be written as a sum of positive squares in 2 ways, for example, as 8976016 + 12730624 = 2996^2 + 3568^2 .

It is a tau number, because it is divible by the number of its divisors (20).

It is a hoax number, since the sum of its digits (26) coincides with the sum of the digits of its distinct prime factors.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 135587 + ... + 135746.

Almost surely, 2^21706640 is an apocalyptic number.

21706640 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21706640 is an abundant number, since it is smaller than the sum of its proper divisors (28761484).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21706640 is a wasteful number, since it uses less digits than its factorization.

21706640 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 271346 (or 271340 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 26.

The square root of 21706640 is about 4659.0385274217. The cubic root of 21706640 is about 278.9528917608.

The spelling of 21706640 in words is "twenty-one million, seven hundred six thousand, six hundred forty".