1218129408721 has 9 divisors (see below), whose sum is σ = 1232069393233. Its totient is φ = 1204345436800.

The previous prime is 1218129408667. The next prime is 1218129408731. The reversal of 1218129408721 is 1278049218121.

The square root of 1218129408721 is 1103689.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 237791794321 + 980337614400 = 487639^2 + 990120^2 .

It is a de Polignac number, because none of the positive numbers 2^k-1218129408721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1218129408731) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 98222121 + ... + 98234521.

Almost surely, 2^{1218129408721} is an apocalyptic number.

1218129408721 is the 1103689-th square number.

1218129408721 is the 551845-th centered octagonal number.

It is an amenable number.

1218129408721 is a deficient number, since it is larger than the sum of its proper divisors (13939984512).

1218129408721 is an frugal number, since it uses more digits than its factorization.

1218129408721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24980 (or 12490 counting only the distinct ones).

The product of its (nonzero) digits is 129024, while the sum is 46.

The spelling of 1218129408721 in words is "one trillion, two hundred eighteen billion, one hundred twenty-nine million, four hundred eight thousand, seven hundred twenty-one".