21450240 has 360 divisors, whose sum is σ = 90965160. Its totient is φ = 4644864.

The previous prime is 21450239. The next prime is 21450241. The reversal of 21450240 is 4205412.

21450240 = T₃₇₇ + T₃₇₈ + ... + T₅₆₆.

It is an interprime number because it is at equal distance from previous prime (21450239) and next prime (21450241).

It is a tau number, because it is divible by the number of its divisors (360).

It is a super-2 number, since 2×21450240² = 920225592115200, which contains 22 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 not an unprimeable number, because it can be changed into a prime (21450241) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 1128951 + ... + 1128969.

It is an arithmetic number, because the mean of its divisors is an integer number (252681).

Almost surely, 2^21450240 is an apocalyptic number.

21450240 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 21450240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (45482580).

21450240 is an abundant number, since it is smaller than the sum of its proper divisors (69514920).

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

21450240 is a wasteful number, since it uses less digits than its factorization.

21450240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 62 (or 36 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21450240 is about 4631.4403807023. The cubic root of 21450240 is about 277.8502031000.

Adding to 21450240 its reverse (4205412), we get a palindrome (25655652).

The spelling of 21450240 in words is "twenty-one million, four hundred fifty thousand, two hundred forty".