131221638 has 48 divisors (see below), whose sum is σ = 306271680. Its totient is φ = 40470192.

The previous prime is 131221637. The next prime is 131221669. The reversal of 131221638 is 836122131.

It is a happy number.

131221638 is a `hidden beast` number, since 1 + 3 + 1 + 2 + 21 + 638 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (131221633) 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, 10245 + ... + 19167.

It is an arithmetic number, because the mean of its divisors is an integer number (6380660).

Almost surely, 2^131221638 is an apocalyptic number.

131221638 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is a practical number, because each smaller number is the sum of distinct divisors of 131221638, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (153135840).

131221638 is an abundant number, since it is smaller than the sum of its proper divisors (175050042).

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

131221638 is a wasteful number, since it uses less digits than its factorization.

131221638 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8993 (or 8990 counting only the distinct ones).

The product of its digits is 1728, while the sum is 27.

The square root of 131221638 is about 11455.2013513513. The cubic root of 131221638 is about 508.1615700136.

Adding to 131221638 its reverse (836122131), we get a palindrome (967343769).

The spelling of 131221638 in words is "one hundred thirty-one million, two hundred twenty-one thousand, six hundred thirty-eight".