1221011100 has 162 divisors, whose sum is σ = 3937393824. Its totient is φ = 316483200.

The previous prime is 1221011093. The next prime is 1221011107. The reversal of 1221011100 is 11101221.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (1221011093) and next prime (1221011107).

It is a Harshad number since it is a multiple of its sum of digits (9).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221011107) by changing a digit.

It is a polite number, since it can be written in 53 ways as a sum of consecutive naturals, for example, 1231605 + ... + 1232595.

Almost surely, 2^1221011100 is an apocalyptic number.

1221011100 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 1221011100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1968696912).

1221011100 is an abundant number, since it is smaller than the sum of its proper divisors (2716382724).

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

1221011100 is a wasteful number, since it uses less digits than its factorization.

1221011100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1085 (or 1038 counting only the distinct ones).

The product of its (nonzero) digits is 4, while the sum is 9.

The square root of 1221011100 is about 34942.9692499078. The cubic root of 1221011100 is about 1068.8248372752.

Adding to 1221011100 its reverse (11101221), we get a palindrome (1232112321).

It can be divided in two parts, 122101 and 1100, that added together give a square (123201 = 351²).

The spelling of 1221011100 in words is "one billion, two hundred twenty-one million, eleven thousand, one hundred".