155965721 has 2 divisors, whose sum is σ = 155965722. Its totient is φ = 155965720.

The previous prime is 155965703. The next prime is 155965723. The reversal of 155965721 is 127569551.

155965721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 144480400 + 11485321 = 12020^2 + 3389^2 .

It is an emirp because it is prime and its reverse (127569551) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 155965721 - 2¹⁸ = 155703577 is a prime.

It is a super-2 number, since 2×155965721² = 48650612254099682, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 155965723, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (155965723) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77982860 + 77982861.

It is an arithmetic number, because the mean of its divisors is an integer number (77982861).

Almost surely, 2^155965721 is an apocalyptic number.

It is an amenable number.

155965721 is a deficient number, since it is larger than the sum of its proper divisors (1).

155965721 is an equidigital number, since it uses as much as digits as its factorization.

155965721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 94500, while the sum is 41.

The square root of 155965721 is about 12488.6236631584. The cubic root of 155965721 is about 538.2818285885.

The spelling of 155965721 in words is "one hundred fifty-five million, nine hundred sixty-five thousand, seven hundred twenty-one".