21691240 has 16 divisors (see below), whose sum is σ = 48805380. Its totient is φ = 8676480.

The previous prime is 21691223. The next prime is 21691247. The reversal of 21691240 is 4219612.

It can be written as a sum of positive squares in 2 ways, for example, as 18472804 + 3218436 = 4298^2 + 1794^2 .

It is not an unprimeable number, because it can be changed into a prime (21691247) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 271101 + ... + 271180.

Almost surely, 2^21691240 is an apocalyptic number.

21691240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21691240 is an abundant number, since it is smaller than the sum of its proper divisors (27114140).

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

21691240 is a wasteful number, since it uses less digits than its factorization.

21691240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 542292 (or 542288 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 25.

The square root of 21691240 is about 4657.3855326782. The cubic root of 21691240 is about 278.8869074836.

The spelling of 21691240 in words is "twenty-one million, six hundred ninety-one thousand, two hundred forty".