21631340 has 24 divisors (see below), whose sum is σ = 45633840. Its totient is φ = 8612928.

The previous prime is 21631321. The next prime is 21631349. The reversal of 21631340 is 4313612.

It is a Harshad number since it is a multiple of its sum of digits (20).

It is not an unprimeable number, because it can be changed into a prime (21631349) 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, 2219 + ... + 6941.

It is an arithmetic number, because the mean of its divisors is an integer number (1901410).

Almost surely, 2^21631340 is an apocalyptic number.

21631340 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21631340 is an abundant number, since it is smaller than the sum of its proper divisors (24002500).

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

21631340 is a wasteful number, since it uses less digits than its factorization.

21631340 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4961 (or 4959 counting only the distinct ones).

The product of its (nonzero) digits is 432, while the sum is 20.

The square root of 21631340 is about 4650.9504405014. The cubic root of 21631340 is about 278.6299569580.

Adding to 21631340 its reverse (4313612), we get a palindrome (25944952).

The spelling of 21631340 in words is "twenty-one million, six hundred thirty-one thousand, three hundred forty".