21415240 has 128 divisors (see below), whose sum is σ = 63763200. Its totient is φ = 6266880.

The previous prime is 21415217. The next prime is 21415249. The reversal of 21415240 is 4251412.

21415240 is a nontrivial binomial coefficient, being equal to C(6545, 2).

It is a super-2 number, since 2×21415240² = 917225008515200, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21415249) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 52156 + ... + 52564.

It is an arithmetic number, because the mean of its divisors is an integer number (498150).

Almost surely, 2^21415240 is an apocalyptic number.

21415240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

21415240 is the 6544-th triangular number.

21415240 is the 2182-nd centered nonagonal number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21415240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31881600).

21415240 is an abundant number, since it is smaller than the sum of its proper divisors (42347960).

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

21415240 is a wasteful number, since it uses less digits than its factorization.

21415240 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 455 (or 451 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 19.

The square root of 21415240 is about 4627.6603159696. The cubic root of 21415240 is about 277.6989996457.

Adding to 21415240 its reverse (4251412), we get a palindrome (25666652).

It can be divided in two parts, 2141 and 5240, that added together give a triangular number (7381 = T₁₂₁).

The spelling of 21415240 in words is "twenty-one million, four hundred fifteen thousand, two hundred forty".