21691590 has 16 divisors (see below), whose sum is σ = 52059888. Its totient is φ = 5784416.

The previous prime is 21691577. The next prime is 21691613. The reversal of 21691590 is 9519612.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 361497 + ... + 361556.

It is an arithmetic number, because the mean of its divisors is an integer number (3253743).

Almost surely, 2^21691590 is an apocalyptic number.

21691590 is an abundant number, since it is smaller than the sum of its proper divisors (30368298).

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

21691590 is a wasteful number, since it uses less digits than its factorization.

21691590 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 723063.

The product of its (nonzero) digits is 4860, while the sum is 33.

The square root of 21691590 is about 4657.4231072558. The cubic root of 21691590 is about 278.8884074730. Note that the first 3 decimals are identical.

It can be divided in two parts, 216 and 91590, that added together give a triangular number (91806 = T₄₂₈).

The spelling of 21691590 in words is "twenty-one million, six hundred ninety-one thousand, five hundred ninety".