915205257721 has 2 divisors, whose sum is σ = 915205257722. Its totient is φ = 915205257720.

The previous prime is 915205257679. The next prime is 915205257731. The reversal of 915205257721 is 127752502519.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 514288345321 + 400916912400 = 717139^2 + 633180^2 .

It is an emirp because it is prime and its reverse (127752502519) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 915205257721 - 2¹⁵ = 915205224953 is a prime.

It is a super-2 number, since 2×915205257721² (a number of 25 digits) contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (915205257731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 457602628860 + 457602628861.

It is an arithmetic number, because the mean of its divisors is an integer number (457602628861).

Almost surely, 2^915205257721 is an apocalyptic number.

It is an amenable number.

915205257721 is a deficient number, since it is larger than the sum of its proper divisors (1).

915205257721 is an equidigital number, since it uses as much as digits as its factorization.

915205257721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 441000, while the sum is 46.

The spelling of 915205257721 in words is "nine hundred fifteen billion, two hundred five million, two hundred fifty-seven thousand, seven hundred twenty-one".