1221515123 has 4 divisors (see below), whose sum is σ = 1239746760. Its totient is φ = 1203283488.

The previous prime is 1221515069. The next prime is 1221515129. The reversal of 1221515123 is 3215151221.

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

It is a cyclic number.

It is not a de Polignac number, because 1221515123 - 2¹⁸ = 1221252979 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1221515129) 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, 9115718 + ... + 9115851.

It is an arithmetic number, because the mean of its divisors is an integer number (309936690).

Almost surely, 2^1221515123 is an apocalyptic number.

1221515123 is a deficient number, since it is larger than the sum of its proper divisors (18231637).

1221515123 is an equidigital number, since it uses as much as digits as its factorization.

1221515123 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18231636.

The product of its digits is 600, while the sum is 23.

The square root of 1221515123 is about 34950.1805860857. The cubic root of 1221515123 is about 1068.9718843120.

Adding to 1221515123 its reverse (3215151221), we get a palindrome (4436666344).

The spelling of 1221515123 in words is "one billion, two hundred twenty-one million, five hundred fifteen thousand, one hundred twenty-three".