1221556056721 has 24 divisors (see below), whose sum is σ = 1652556460352. Its totient is φ = 878641711200.

The previous prime is 1221556056719. The next prime is 1221556056751. The reversal of 1221556056721 is 1276506551221.

It is not a de Polignac number, because 1221556056721 - 2¹ = 1221556056719 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1221556056751) 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, 55458795 + ... + 55480816.

Almost surely, 2^{1221556056721} is an apocalyptic number.

1221556056721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1221556056721 is a deficient number, since it is larger than the sum of its proper divisors (431000403631).

1221556056721 is a wasteful number, since it uses less digits than its factorization.

1221556056721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 110939653 (or 110939642 counting only the distinct ones).

The product of its (nonzero) digits is 252000, while the sum is 43.

The spelling of 1221556056721 in words is "one trillion, two hundred twenty-one billion, five hundred fifty-six million, fifty-six thousand, seven hundred twenty-one".