21691280 has 40 divisors (see below), whose sum is σ = 54314232. Its totient is φ = 8008704.

The previous prime is 21691279. The next prime is 21691283. The reversal of 21691280 is 8219612.

It can be written as a sum of positive squares in 4 ways, for example, as 3984016 + 17707264 = 1996^2 + 4208^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is not an unprimeable number, because it can be changed into a prime (21691283) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 9389 + ... + 11468.

Almost surely, 2^21691280 is an apocalyptic number.

21691280 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21691280 is an abundant number, since it is smaller than the sum of its proper divisors (32622952).

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

21691280 is a wasteful number, since it uses less digits than its factorization.

21691280 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20883 (or 20877 counting only the distinct ones).

The product of its (nonzero) digits is 1728, while the sum is 29.

The square root of 21691280 is about 4657.3898269310. The cubic root of 21691280 is about 278.8870789118.

The spelling of 21691280 in words is "twenty-one million, six hundred ninety-one thousand, two hundred eighty".