1220721657 has 4 divisors (see below), whose sum is σ = 1627628880. Its totient is φ = 813814436.

The previous prime is 1220721641. The next prime is 1220721661. The reversal of 1220721657 is 7561270221.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 7561270221 = 3 ⋅2520423407.

It is a cyclic number.

It is not a de Polignac number, because 1220721657 - 2⁴ = 1220721641 is a prime.

It is a super-2 number, since 2×1220721657² = 2980322727737651298, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (1220723657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 203453607 + ... + 203453612.

It is an arithmetic number, because the mean of its divisors is an integer number (406907220).

Almost surely, 2^1220721657 is an apocalyptic number.

It is an amenable number.

1220721657 is a deficient number, since it is larger than the sum of its proper divisors (406907223).

1220721657 is an equidigital number, since it uses as much as digits as its factorization.

1220721657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 406907222.

The product of its (nonzero) digits is 11760, while the sum is 33.

The square root of 1220721657 is about 34938.8273558229. The cubic root of 1220721657 is about 1068.7403749484.

Adding to 1220721657 its reverse (7561270221), we get a palindrome (8781991878).

The spelling of 1220721657 in words is "one billion, two hundred twenty million, seven hundred twenty-one thousand, six hundred fifty-seven".