21731130 has 48 divisors (see below), whose sum is σ = 57156840. Its totient is φ = 5727744.

The previous prime is 21731123. The next prime is 21731131. The reversal of 21731130 is 3113712.

It can be written as a sum of positive squares in 4 ways, for example, as 19900521 + 1830609 = 4461^2 + 1353^2 .

It is a super-2 number, since 2×21731130² = 944484022153800, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21731131) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 6654 + ... + 9366.

Almost surely, 2^21731130 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21731130, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (28578420).

21731130 is an abundant number, since it is smaller than the sum of its proper divisors (35425710).

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

21731130 is a wasteful number, since it uses less digits than its factorization.

21731130 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2815 (or 2812 counting only the distinct ones).

The product of its (nonzero) digits is 126, while the sum is 18.

The square root of 21731130 is about 4661.6660112024. Note that the first 3 decimals coincide. The cubic root of 21731130 is about 279.0577596529.

Adding to 21731130 its reverse (3113712), we get a palindrome (24844842).

The spelling of 21731130 in words is "twenty-one million, seven hundred thirty-one thousand, one hundred thirty".