1221212220 has 48 divisors (see below), whose sum is σ = 3483920160. Its totient is φ = 319511296.

The previous prime is 1221212219. The next prime is 1221212281. The reversal of 1221212220 is 222121221.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a self number, because there is not a number n which added to its sum of digits gives 1221212220.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 188835 + ... + 195194.

It is an arithmetic number, because the mean of its divisors is an integer number (72581670).

Almost surely, 2^1221212220 is an apocalyptic number.

1221212220 is a gapful number since it is divisible by the number (10) formed by its first and last digit.

It is an amenable number.

1221212220 is an abundant number, since it is smaller than the sum of its proper divisors (2262707940).

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

1221212220 is a wasteful number, since it uses less digits than its factorization.

1221212220 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 384094 (or 384092 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 15.

The square root of 1221212220 is about 34945.8469635520. The cubic root of 1221212220 is about 1068.8835182186.

Adding to 1221212220 its reverse (222121221), we get a palindrome (1443333441).

Subtracting from 1221212220 its reverse (222121221), we obtain a palindrome (999090999).

The spelling of 1221212220 in words is "one billion, two hundred twenty-one million, two hundred twelve thousand, two hundred twenty".