155520721 has 2 divisors, whose sum is σ = 155520722. Its totient is φ = 155520720.

The previous prime is 155520713. The next prime is 155520737. The reversal of 155520721 is 127025551.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 115261696 + 40259025 = 10736^2 + 6345^2 .

It is a cyclic number.

It is not a de Polignac number, because 155520721 - 2³ = 155520713 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 155520721.

It is not a weakly prime, because it can be changed into another prime (155520221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77760360 + 77760361.

It is an arithmetic number, because the mean of its divisors is an integer number (77760361).

Almost surely, 2^155520721 is an apocalyptic number.

It is an amenable number.

155520721 is a deficient number, since it is larger than the sum of its proper divisors (1).

155520721 is an equidigital number, since it uses as much as digits as its factorization.

155520721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3500, while the sum is 28.

The square root of 155520721 is about 12470.7947220696. The cubic root of 155520721 is about 537.7694006280.

The spelling of 155520721 in words is "one hundred fifty-five million, five hundred twenty thousand, seven hundred twenty-one".