251491217121 has 15 divisors (see below), whose sum is σ = 375691153123. Its totient is φ = 167657802480.

The previous prime is 251491217083. The next prime is 251491217123. The reversal of 251491217121 is 121712194152.

It is a happy number.

The square root of 251491217121 is 501489.

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

251491217121 is a `hidden beast` number, since 2 + 514 + 9 + 1 + 2 + 17 + 121 = 666.

It can be written as a sum of positive squares in only one way, i.e., 251040079521 + 451137600 = 501039^2 + 21240^2 .

It is not a de Polignac number, because 251491217121 - 2¹⁹ = 251490692833 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (251491217123) by changing a digit.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 4485541 + ... + 4541261.

Almost surely, 2^251491217121 is an apocalyptic number.

251491217121 is the 501489-th square number.

251491217121 is the 250745-th centered octagonal number.

It is an amenable number.

251491217121 is a deficient number, since it is larger than the sum of its proper divisors (124199936002).

251491217121 is an frugal number, since it uses more digits than its factorization.

251491217121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 111454 (or 55724 counting only the distinct ones).

The product of its digits is 10080, while the sum is 36.

Multiplying 251491217121 by its sum of digits (36), we get a square (9053683816356 = 3008934²).

The spelling of 251491217121 in words is "two hundred fifty-one billion, four hundred ninety-one million, two hundred seventeen thousand, one hundred twenty-one".