155440021 has 4 divisors (see below), whose sum is σ = 169570944. Its totient is φ = 141309100.

The previous prime is 155440009. The next prime is 155440037. The reversal of 155440021 is 120044551.

155440021 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 120044551 = 11 ⋅10913141.

It is a cyclic number.

It is not a de Polignac number, because 155440021 - 2⁹ = 155439509 is a prime.

It is a Smith number, since the sum of its digits (22) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 155439974 and 155440001.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155440091) 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, 7065445 + ... + 7065466.

It is an arithmetic number, because the mean of its divisors is an integer number (42392736).

Almost surely, 2^155440021 is an apocalyptic number.

155440021 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

155440021 is a deficient number, since it is larger than the sum of its proper divisors (14130923).

155440021 is a wasteful number, since it uses less digits than its factorization.

155440021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14130922.

The product of its (nonzero) digits is 800, while the sum is 22.

The square root of 155440021 is about 12467.5587425927. The cubic root of 155440021 is about 537.6763680105.

Adding to 155440021 its reverse (120044551), we get a palindrome (275484572).

The spelling of 155440021 in words is "one hundred fifty-five million, four hundred forty thousand, twenty-one".