1221511155 has 32 divisors (see below), whose sum is σ = 2056235328. Its totient is φ = 618393600.

The previous prime is 1221511141. The next prime is 1221511157. The reversal of 1221511155 is 5511151221.

It is not a de Polignac number, because 1221511155 - 2⁹ = 1221510643 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1221511157) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 4086 + ... + 49595.

It is an arithmetic number, because the mean of its divisors is an integer number (64257354).

Almost surely, 2^1221511155 is an apocalyptic number.

1221511155 is a gapful number since it is divisible by the number (15) formed by its first and last digit.

1221511155 is a deficient number, since it is larger than the sum of its proper divisors (834724173).

1221511155 is a wasteful number, since it uses less digits than its factorization.

1221511155 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53767.

The product of its digits is 500, while the sum is 24.

The square root of 1221511155 is about 34950.1238195232. The cubic root of 1221511155 is about 1068.9707268192.

Adding to 1221511155 its reverse (5511151221), we get a palindrome (6732662376).

The spelling of 1221511155 in words is "one billion, two hundred twenty-one million, five hundred eleven thousand, one hundred fifty-five".