1221903721 has 4 divisors (see below), whose sum is σ = 1223378500. Its totient is φ = 1220428944.

The previous prime is 1221903701. The next prime is 1221903751. The reversal of 1221903721 is 1273091221.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 485541225 + 736362496 = 22035^2 + 27136^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221903721 - 2⁷ = 1221903593 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1221903721.

It is not an unprimeable number, because it can be changed into a prime (1221903701) 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, 736146 + ... + 737803.

It is an arithmetic number, because the mean of its divisors is an integer number (305844625).

Almost surely, 2^1221903721 is an apocalyptic number.

It is an amenable number.

1221903721 is a deficient number, since it is larger than the sum of its proper divisors (1474779).

1221903721 is an equidigital number, since it uses as much as digits as its factorization.

1221903721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1474778.

The product of its (nonzero) digits is 1512, while the sum is 28.

The square root of 1221903721 is about 34955.7394572050. The cubic root of 1221903721 is about 1069.0852288752.

Adding to 1221903721 its reverse (1273091221), we get a palindrome (2494994942).

The spelling of 1221903721 in words is "one billion, two hundred twenty-one million, nine hundred three thousand, seven hundred twenty-one".