155207221 has 4 divisors (see below), whose sum is σ = 167146252. Its totient is φ = 143268192.

The previous prime is 155207209. The next prime is 155207233. The reversal of 155207221 is 122702551.

It is a semiprime because it is the product of two primes.

It is an interprime number because it is at equal distance from previous prime (155207209) and next prime (155207233).

It can be written as a sum of positive squares in 2 ways, for example, as 72488196 + 82719025 = 8514^2 + 9095^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-155207221 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155207251) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5969496 + ... + 5969521.

It is an arithmetic number, because the mean of its divisors is an integer number (41786563).

Almost surely, 2^155207221 is an apocalyptic number.

It is an amenable number.

155207221 is a deficient number, since it is larger than the sum of its proper divisors (11939031).

155207221 is a wasteful number, since it uses less digits than its factorization.

155207221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11939030.

The product of its (nonzero) digits is 1400, while the sum is 25.

The square root of 155207221 is about 12458.2190139682. The cubic root of 155207221 is about 537.4078108341.

Adding to 155207221 its reverse (122702551), we get a palindrome (277909772).

The spelling of 155207221 in words is "one hundred fifty-five million, two hundred seven thousand, two hundred twenty-one".