1221608061721 has 4 divisors (see below), whose sum is σ = 1221767112244. Its totient is φ = 1221449011200.

The previous prime is 1221608061703. The next prime is 1221608061731. The reversal of 1221608061721 is 1271608061221.

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

It can be written as a sum of positive squares in 2 ways, for example, as 1100233166400 + 121374895321 = 1048920^2 + 348389^2 .

It is a cyclic number.

It is not a de Polignac number, because 1221608061721 - 2²¹ = 1221605964569 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1221608061731) 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, 79513740 + ... + 79529101.

It is an arithmetic number, because the mean of its divisors is an integer number (305441778061).

Almost surely, 2^{1221608061721} is an apocalyptic number.

It is an amenable number.

1221608061721 is a deficient number, since it is larger than the sum of its proper divisors (159050523).

1221608061721 is an equidigital number, since it uses as much as digits as its factorization.

1221608061721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 159050522.

The product of its (nonzero) digits is 16128, while the sum is 37.

The spelling of 1221608061721 in words is "one trillion, two hundred twenty-one billion, six hundred eight million, sixty-one thousand, seven hundred twenty-one".