1216721025 has 72 divisors (see below), whose sum is σ = 2485075320. Its totient is φ = 563742720.

The previous prime is 1216720969. The next prime is 1216721039. The reversal of 1216721025 is 5201276121.

It can be written as a sum of positive squares in 12 ways, for example, as 600887169 + 615833856 = 24513^2 + 24816^2 .

It is not a de Polignac number, because 1216721025 - 2²⁴ = 1199943809 is a prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 1216721025.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 37491 + ... + 61959.

It is an arithmetic number, because the mean of its divisors is an integer number (34514935).

Almost surely, 2^1216721025 is an apocalyptic number.

1216721025 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

It is an amenable number.

1216721025 is an abundant number, since it is smaller than the sum of its proper divisors (1268354295).

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

1216721025 is a wasteful number, since it uses less digits than its factorization.

1216721025 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24515 (or 24507 counting only the distinct ones).

The product of its (nonzero) digits is 1680, while the sum is 27.

The square root of 1216721025 is about 34881.5284212146. The cubic root of 1216721025 is about 1067.5715809964.

Adding to 1216721025 its reverse (5201276121), we get a palindrome (6417997146).

The spelling of 1216721025 in words is "one billion, two hundred sixteen million, seven hundred twenty-one thousand, twenty-five".