915172721 has 2 divisors, whose sum is σ = 915172722. Its totient is φ = 915172720.

The previous prime is 915172717. The next prime is 915172729. The reversal of 915172721 is 127271519.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 837292096 + 77880625 = 28936^2 + 8825^2 .

It is a cyclic number.

It is not a de Polignac number, because 915172721 - 2² = 915172717 is a prime.

It is a super-2 number, since 2×915172721² = 1675082218525087682, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (915172729) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 457586360 + 457586361.

It is an arithmetic number, because the mean of its divisors is an integer number (457586361).

Almost surely, 2^915172721 is an apocalyptic number.

It is an amenable number.

915172721 is a deficient number, since it is larger than the sum of its proper divisors (1).

915172721 is an equidigital number, since it uses as much as digits as its factorization.

915172721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 8820, while the sum is 35.

The square root of 915172721 is about 30251.8217798532. The cubic root of 915172721 is about 970.8847707172.

The spelling of 915172721 in words is "nine hundred fifteen million, one hundred seventy-two thousand, seven hundred twenty-one".