1221776721 has 48 divisors (see below), whose sum is σ = 2019244032. Its totient is φ = 704642400.

The previous prime is 1221776719. The next prime is 1221776737. The reversal of 1221776721 is 1276771221.

It is not a de Polignac number, because 1221776721 - 2¹ = 1221776719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1221776701) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 479176 + ... + 481718.

It is an arithmetic number, because the mean of its divisors is an integer number (42067584).

Almost surely, 2^1221776721 is an apocalyptic number.

1221776721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1221776721 is a deficient number, since it is larger than the sum of its proper divisors (797467311).

1221776721 is a wasteful number, since it uses less digits than its factorization.

1221776721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2794 (or 2791 counting only the distinct ones).

The product of its digits is 16464, while the sum is 36.

The square root of 1221776721 is about 34953.9228270591. The cubic root of 1221776721 is about 1069.0481887151.

The spelling of 1221776721 in words is "one billion, two hundred twenty-one million, seven hundred seventy-six thousand, seven hundred twenty-one".