155640021 has 4 divisors (see below), whose sum is σ = 207520032. Its totient is φ = 103760012.

The previous prime is 155640007. The next prime is 155640029. The reversal of 155640021 is 120046551.

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.

It is a cyclic number.

It is not a de Polignac number, because 155640021 - 2¹³ = 155631829 is a prime.

It is a super-2 number, since 2×155640021² = 48447632273760882, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 155639973 and 155640000.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155640029) 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 3 ways as a sum of consecutive naturals, for example, 25940001 + ... + 25940006.

It is an arithmetic number, because the mean of its divisors is an integer number (51880008).

Almost surely, 2^155640021 is an apocalyptic number.

It is an amenable number.

155640021 is a deficient number, since it is larger than the sum of its proper divisors (51880011).

155640021 is an equidigital number, since it uses as much as digits as its factorization.

155640021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 51880010.

The product of its (nonzero) digits is 1200, while the sum is 24.

The square root of 155640021 is about 12475.5769806450. The cubic root of 155640021 is about 537.9068731813.

Adding to 155640021 its reverse (120046551), we get a palindrome (275686572).

The spelling of 155640021 in words is "one hundred fifty-five million, six hundred forty thousand, twenty-one".