1221221661 has 24 divisors (see below), whose sum is σ = 1799764512. Its totient is φ = 736005600.

The previous prime is 1221221653. The next prime is 1221221717. The reversal of 1221221661 is 1661221221.

It is not a de Polignac number, because 1221221661 - 2³ = 1221221653 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221221621) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 56410 + ... + 74996.

It is an arithmetic number, because the mean of its divisors is an integer number (74990188).

Almost surely, 2^1221221661 is an apocalyptic number.

1221221661 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1221221661 is a deficient number, since it is larger than the sum of its proper divisors (578542851).

1221221661 is a wasteful number, since it uses less digits than its factorization.

1221221661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 18793 (or 18782 counting only the distinct ones).

The product of its digits is 576, while the sum is 24.

The square root of 1221221661 is about 34945.9820437200. The cubic root of 1221221661 is about 1068.8862726684.

Adding to 1221221661 its reverse (1661221221), we get a palindrome (2882442882).

The spelling of 1221221661 in words is "one billion, two hundred twenty-one million, two hundred twenty-one thousand, six hundred sixty-one".