1221347661 has 16 divisors (see below), whose sum is σ = 1647651264. Its totient is φ = 804662784.

The previous prime is 1221347639. The next prime is 1221347671. The reversal of 1221347661 is 1667431221.

It is not a de Polignac number, because 1221347661 - 2¹⁷ = 1221216589 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1221347671) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 226351 + ... + 231683.

It is an arithmetic number, because the mean of its divisors is an integer number (102978204).

Almost surely, 2^1221347661 is an apocalyptic number.

It is an amenable number.

1221347661 is a deficient number, since it is larger than the sum of its proper divisors (426303603).

1221347661 is an equidigital number, since it uses as much as digits as its factorization.

1221347661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6220.

The product of its digits is 12096, while the sum is 33.

The square root of 1221347661 is about 34947.7847795822. The cubic root of 1221347661 is about 1068.9230323174.

Adding to 1221347661 its reverse (1667431221), we get a palindrome (2888778882).

It can be divided in two parts, 122134 and 7661, that added together give a triangular number (129795 = T₅₀₉).

The spelling of 1221347661 in words is "one billion, two hundred twenty-one million, three hundred forty-seven thousand, six hundred sixty-one".