21991340 has 24 divisors (see below), whose sum is σ = 52779552. Its totient is φ = 7539840.

The previous prime is 21991313. The next prime is 21991349. The reversal of 21991340 is 4319912.

It is a happy number.

It is not an unprimeable number, because it can be changed into a prime (21991349) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 78401 + ... + 78680.

It is an arithmetic number, because the mean of its divisors is an integer number (2199148).

Almost surely, 2^21991340 is an apocalyptic number.

21991340 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21991340 is an abundant number, since it is smaller than the sum of its proper divisors (30788212).

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

21991340 is a wasteful number, since it uses less digits than its factorization.

21991340 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 157097 (or 157095 counting only the distinct ones).

The product of its (nonzero) digits is 1944, while the sum is 29.

The square root of 21991340 is about 4689.4925098565. The cubic root of 21991340 is about 280.1671620879.

The spelling of 21991340 in words is "twenty-one million, nine hundred ninety-one thousand, three hundred forty".