1221111100 has 72 divisors (see below), whose sum is σ = 2897345808. Its totient is φ = 443020800.

The previous prime is 1221111097. The next prime is 1221111167. The reversal of 1221111100 is 11111221.

It is a super-2 number, since 2×1221111100² = 2982224637086420000, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (10).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 611704 + ... + 613696.

It is an arithmetic number, because the mean of its divisors is an integer number (40240914).

Almost surely, 2^1221111100 is an apocalyptic number.

1221111100 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 1221111100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1448672904).

1221111100 is an abundant number, since it is smaller than the sum of its proper divisors (1676234708).

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

1221111100 is a wasteful number, since it uses less digits than its factorization.

1221111100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2575 (or 2568 counting only the distinct ones).

The product of its (nonzero) digits is 4, while the sum is 10.

The square root of 1221111100 is about 34944.4001236250. The cubic root of 1221111100 is about 1068.8540151606.

Adding to 1221111100 its reverse (11111221), we get a palindrome (1232222321).

It can be divided in two parts, 12 and 21111100, that added together give a palindrome (21111112).

The spelling of 1221111100 in words is "one billion, two hundred twenty-one million, one hundred eleven thousand, one hundred".