21121440 has 96 divisors (see below), whose sum is σ = 67495680. Its totient is φ = 5551104.

The previous prime is 21121417. The next prime is 21121453. The reversal of 21121440 is 4412112.

21121440 = T₁₀₉ + T₁₁₀ + ... + T₅₀₃.

It is a tau number, because it is divible by the number of its divisors (96).

It is a super-2 number, since 2×21121440² = 892230455347200, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37642 + ... + 38198.

It is an arithmetic number, because the mean of its divisors is an integer number (703080).

Almost surely, 2^21121440 is an apocalyptic number.

21121440 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 21121440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33747840).

21121440 is an abundant number, since it is smaller than the sum of its proper divisors (46374240).

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

21121440 is a wasteful number, since it uses less digits than its factorization.

21121440 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 654 (or 646 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 15.

The square root of 21121440 is about 4595.8067844504. The cubic root of 21121440 is about 276.4232112606.

Adding to 21121440 its reverse (4412112), we get a palindrome (25533552).

The spelling of 21121440 in words is "twenty-one million, one hundred twenty-one thousand, four hundred forty".