155540021 has 32 divisors (see below), whose sum is σ = 209744640. Its totient is φ = 111799296.

The previous prime is 155540009. The next prime is 155540039. The reversal of 155540021 is 120045551.

It is a happy number.

It is not a de Polignac number, because 155540021 - 2¹⁴ = 155523637 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155540221) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 43130 + ... + 46596.

It is an arithmetic number, because the mean of its divisors is an integer number (6554520).

Almost surely, 2^155540021 is an apocalyptic number.

It is an amenable number.

155540021 is a deficient number, since it is larger than the sum of its proper divisors (54204619).

155540021 is a wasteful number, since it uses less digits than its factorization.

155540021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3533.

The product of its (nonzero) digits is 1000, while the sum is 23.

The square root of 155540021 is about 12471.5685060060. The cubic root of 155540021 is about 537.7916452953.

Adding to 155540021 its reverse (120045551), we get a palindrome (275585572).

The spelling of 155540021 in words is "one hundred fifty-five million, five hundred forty thousand, twenty-one".