21660156 has 72 divisors (see below), whose sum is σ = 65340240. Its totient is φ = 6187104.

The previous prime is 21660151. The next prime is 21660161. The reversal of 21660156 is 65106612.

It is a happy number.

21660156 is a `hidden beast` number, since 2 + 1 + 6 + 601 + 56 = 666.

It is an interprime number because it is at equal distance from previous prime (21660151) and next prime (21660161).

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21660151) 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, 3246 + ... + 7338.

Almost surely, 2^21660156 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21660156, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32670120).

21660156 is an abundant number, since it is smaller than the sum of its proper divisors (43680084).

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

21660156 is a wasteful number, since it uses less digits than its factorization.

21660156 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4120 (or 4105 counting only the distinct ones).

The product of its (nonzero) digits is 2160, while the sum is 27.

The square root of 21660156 is about 4654.0472709245. The cubic root of 21660156 is about 278.7536268774.

Adding to 21660156 its reverse (65106612), we get a palindrome (86766768).

The spelling of 21660156 in words is "twenty-one million, six hundred sixty thousand, one hundred fifty-six".