155721011 has 4 divisors (see below), whose sum is σ = 159034272. Its totient is φ = 152407752.

The previous prime is 155720989. The next prime is 155721019. The reversal of 155721011 is 110127551.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 110127551 = 2957 ⋅37243.

It is a cyclic number.

It is not a de Polignac number, because 155721011 - 2⁶ = 155720947 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (155721019) 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, 1656560 + ... + 1656653.

It is an arithmetic number, because the mean of its divisors is an integer number (39758568).

Almost surely, 2^155721011 is an apocalyptic number.

155721011 is a deficient number, since it is larger than the sum of its proper divisors (3313261).

155721011 is an equidigital number, since it uses as much as digits as its factorization.

155721011 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3313260.

The product of its (nonzero) digits is 350, while the sum is 23.

The square root of 155721011 is about 12478.8225005407. The cubic root of 155721011 is about 538.0001600770. Note that the first 3 decimals are identical.

Adding to 155721011 its reverse (110127551), we get a palindrome (265848562).

The spelling of 155721011 in words is "one hundred fifty-five million, seven hundred twenty-one thousand, eleven".