1221538500 has 576 divisors, whose sum is σ = 5024248320. Its totient is φ = 242611200.

The previous prime is 1221538499. The next prime is 1221538501. The reversal of 1221538500 is 58351221.

It is a happy number.

1221538500 is a `hidden beast` number, since 1 + 2 + 2 + 153 + 8 + 500 = 666.

It is an interprime number because it is at equal distance from previous prime (1221538499) and next prime (1221538501).

It is not an unprimeable number, because it can be changed into a prime (1221538501) by changing a digit.

It is a polite number, since it can be written in 191 ways as a sum of consecutive naturals, for example, 7780422 + ... + 7780578.

Almost surely, 2^1221538500 is an apocalyptic number.

1221538500 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 1221538500, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2512124160).

1221538500 is an abundant number, since it is smaller than the sum of its proper divisors (3802709820).

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

1221538500 is a wasteful number, since it uses less digits than its factorization.

1221538500 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 221 (or 206 counting only the distinct ones).

The product of its (nonzero) digits is 2400, while the sum is 27.

The square root of 1221538500 is about 34950.5150176646. The cubic root of 1221538500 is about 1068.9787034925.

Adding to 1221538500 its reverse (58351221), we get a palindrome (1279889721).

The spelling of 1221538500 in words is "one billion, two hundred twenty-one million, five hundred thirty-eight thousand, five hundred".