21621240 has 192 divisors, whose sum is σ = 77220000. Its totient is φ = 5225472.

The previous prime is 21621239. The next prime is 21621277. The reversal of 21621240 is 4212612.

21621240 is a `hidden beast` number, since 2 + 1 + 621 + 2 + 40 = 666.

It is a super-3 number, since 3×21621240³ (a number of 23 digits) contains 333 as substring.

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 198306 + ... + 198414.

Almost surely, 2^21621240 is an apocalyptic number.

21621240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21621240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (38610000).

21621240 is an abundant number, since it is smaller than the sum of its proper divisors (55598760).

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

21621240 is a wasteful number, since it uses less digits than its factorization.

21621240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 174 (or 167 counting only the distinct ones).

The product of its (nonzero) digits is 192, while the sum is 18.

The square root of 21621240 is about 4649.8645141552. The cubic root of 21621240 is about 278.5865846924.

Adding to 21621240 its reverse (4212612), we get a palindrome (25833852).

The spelling of 21621240 in words is "twenty-one million, six hundred twenty-one thousand, two hundred forty".