1221638400 has 324 divisors, whose sum is σ = 4428383232. Its totient is φ = 321269760.

The previous prime is 1221638389. The next prime is 1221638423. The reversal of 1221638400 is 48361221.

1221638400 is a `hidden beast` number, since 1 + 2 + 21 + 638 + 4 + 0 + 0 = 666.

It is a super-3 number, since 3×1221638400³ (a number of 28 digits) contains 333 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 7315117 + ... + 7315283.

Almost surely, 2^1221638400 is an apocalyptic number.

1221638400 is a gapful number since it is divisible by the number (10) 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 1221638400, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2214191616).

1221638400 is an abundant number, since it is smaller than the sum of its proper divisors (3206744832).

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

1221638400 is a wasteful number, since it uses less digits than its factorization.

1221638400 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 326 (or 304 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 27.

The square root of 1221638400 is about 34951.9441519352. The cubic root of 1221638400 is about 1069.0078438106.

Adding to 1221638400 its reverse (48361221), we get a palindrome (1269999621).

The spelling of 1221638400 in words is "one billion, two hundred twenty-one million, six hundred thirty-eight thousand, four hundred".