1221145555 has 16 divisors (see below), whose sum is σ = 1747528704. Its totient is φ = 800949600.

The previous prime is 1221145537. The next prime is 1221145567. The reversal of 1221145555 is 5555411221.

It is not a de Polignac number, because 1221145555 - 2⁹ = 1221145043 is a prime.

It is a Duffinian number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 757671 + ... + 759280.

It is an arithmetic number, because the mean of its divisors is an integer number (109220544).

Almost surely, 2^1221145555 is an apocalyptic number.

1221145555 is a deficient number, since it is larger than the sum of its proper divisors (526383149).

1221145555 is a wasteful number, since it uses less digits than its factorization.

1221145555 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1516986.

The product of its digits is 10000, while the sum is 31.

The square root of 1221145555 is about 34944.8931175930. The cubic root of 1221145555 is about 1068.8640680321.

Adding to 1221145555 its reverse (5555411221), we get a palindrome (6776556776).

The spelling of 1221145555 in words is "one billion, two hundred twenty-one million, one hundred forty-five thousand, five hundred fifty-five".