1220721 has 4 divisors (see below), whose sum is σ = 1627632. Its totient is φ = 813812.

The previous prime is 1220717. The next prime is 1220729. The reversal of 1220721 is 1270221.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1220721 - 2² = 1220717 is a prime.

It is a D-number.

1220721 is a lucky number.

It is a self number, because there is not a number n which added to its sum of digits gives 1220721.

It is not an unprimeable number, because it can be changed into a prime (1220729) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 203451 + ... + 203456.

It is an arithmetic number, because the mean of its divisors is an integer number (406908).

2^1220721 is an apocalyptic number.

It is an amenable number.

1220721 is a deficient number, since it is larger than the sum of its proper divisors (406911).

1220721 is an equidigital number, since it uses as much as digits as its factorization.

1220721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 406910.

The product of its (nonzero) digits is 56, while the sum is 15.

The square root of 1220721 is about 1104.8624348759. The cubic root of 1220721 is about 106.8740183214.

Adding to 1220721 its reverse (1270221), we get a palindrome (2490942).

The spelling of 1220721 in words is "one million, two hundred twenty thousand, seven hundred twenty-one".