155445721 has 2 divisors, whose sum is σ = 155445722. Its totient is φ = 155445720.

The previous prime is 155445673. The next prime is 155445757. The reversal of 155445721 is 127544551.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 150405696 + 5040025 = 12264^2 + 2245^2 .

It is an emirp because it is prime and its reverse (127544551) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 155445721 - 2¹⁵ = 155412953 is a prime.

It is equal to p_8733157 and since 155445721 and 8733157 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (155445761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 77722860 + 77722861.

It is an arithmetic number, because the mean of its divisors is an integer number (77722861).

Almost surely, 2^155445721 is an apocalyptic number.

It is an amenable number.

155445721 is a deficient number, since it is larger than the sum of its proper divisors (1).

155445721 is an equidigital number, since it uses as much as digits as its factorization.

155445721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 28000, while the sum is 34.

The square root of 155445721 is about 12467.7873337654. The cubic root of 155445721 is about 537.6829401443.

The spelling of 155445721 in words is "one hundred fifty-five million, four hundred forty-five thousand, seven hundred twenty-one".