1221212100 has 72 divisors (see below), whose sum is σ = 3539023488. Its totient is φ = 325136000.

The previous prime is 1221212089. The next prime is 1221212143. The reversal of 1221212100 is 12121221.

It is a Harshad number since it is a multiple of its sum of digits (12).

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, 207397 + ... + 213203.

It is an arithmetic number, because the mean of its divisors is an integer number (49153104).

Almost surely, 2^1221212100 is an apocalyptic number.

1221212100 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 1221212100, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1769511744).

1221212100 is an abundant number, since it is smaller than the sum of its proper divisors (2317811388).

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

1221212100 is a wasteful number, since it uses less digits than its factorization.

1221212100 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6525 (or 6518 counting only the distinct ones).

The product of its (nonzero) digits is 16, while the sum is 12.

The square root of 1221212100 is about 34945.8452466098. The cubic root of 1221212100 is about 1068.8834832080.

Adding to 1221212100 its reverse (12121221), we get a palindrome (1233333321).

The spelling of 1221212100 in words is "one billion, two hundred twenty-one million, two hundred twelve thousand, one hundred".