1221001561651 has 4 divisors (see below), whose sum is σ = 1221005687904. Its totient is φ = 1220997435400.

The previous prime is 1221001561643. The next prime is 1221001561679. The reversal of 1221001561651 is 1561651001221.

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

It is a cyclic number.

It is not a de Polignac number, because 1221001561651 - 2³ = 1221001561643 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1221001561631) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1581835 + ... + 2223556.

It is an arithmetic number, because the mean of its divisors is an integer number (305251421976).

Almost surely, 2^{1221001561651} is an apocalyptic number.

1221001561651 is a deficient number, since it is larger than the sum of its proper divisors (4126253).

1221001561651 is an equidigital number, since it uses as much as digits as its factorization.

1221001561651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4126252.

The product of its (nonzero) digits is 3600, while the sum is 31.

Adding to 1221001561651 its reverse (1561651001221), we get a palindrome (2782652562872).

The spelling of 1221001561651 in words is "one trillion, two hundred twenty-one billion, one million, five hundred sixty-one thousand, six hundred fifty-one".