1388780721 has 14 divisors (see below), whose sum is σ = 2082219650. Its totient is φ = 925853328.

The previous prime is 1388780693. The next prime is 1388780747. The reversal of 1388780721 is 1270878831.

It can be written as a sum of positive squares in only one way, i.e., 1126340721 + 262440000 = 33561^2 + 16200^2 .

It is not a de Polignac number, because 1388780721 - 2⁷ = 1388780593 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1388780791) by changing a digit.

It is a polite number, since it can be written in 13 ways as a sum of consecutive naturals, for example, 951796 + ... + 953253.

It is an arithmetic number, because the mean of its divisors is an integer number (148729975).

Almost surely, 2^1388780721 is an apocalyptic number.

It is an amenable number.

1388780721 is a deficient number, since it is larger than the sum of its proper divisors (693438929).

1388780721 is an frugal number, since it uses more digits than its factorization.

1388780721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1905067 (or 1905052 counting only the distinct ones).

The product of its (nonzero) digits is 150528, while the sum is 45.

The square root of 1388780721 is about 37266.3483722245. The cubic root of 1388780721 is about 1115.6926182587.

The spelling of 1388780721 in words is "one billion, three hundred eighty-eight million, seven hundred eighty thousand, seven hundred twenty-one".