1221166720 has 64 divisors (see below), whose sum is σ = 2933511840. Its totient is φ = 486097920.

The previous prime is 1221166717. The next prime is 1221166733. The reversal of 1221166720 is 276611221.

It is a tau number, because it is divible by the number of its divisors (64).

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 130519 + ... + 139561.

Almost surely, 2^1221166720 is an apocalyptic number.

1221166720 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 1221166720, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1466755920).

1221166720 is an abundant number, since it is smaller than the sum of its proper divisors (1712345120).

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

1221166720 is an equidigital number, since it uses as much as digits as its factorization.

1221166720 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9273 (or 9261 counting only the distinct ones).

The product of its (nonzero) digits is 2016, while the sum is 28.

The square root of 1221166720 is about 34945.1959502304. The cubic root of 1221166720 is about 1068.8702432111.

Adding to 1221166720 its reverse (276611221), we get a palindrome (1497777941).

The spelling of 1221166720 in words is "one billion, two hundred twenty-one million, one hundred sixty-six thousand, seven hundred twenty".