1561121657 has 2 divisors, whose sum is σ = 1561121658. Its totient is φ = 1561121656.

The previous prime is 1561121623. The next prime is 1561121671. The reversal of 1561121657 is 7561211651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 878292496 + 682829161 = 29636^2 + 26131^2 .

It is a cyclic number.

It is not a de Polignac number, because 1561121657 - 2⁶ = 1561121593 is a prime.

It is not a weakly prime, because it can be changed into another prime (1561121557) 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 as a sum of consecutive naturals, namely, 780560828 + 780560829.

It is an arithmetic number, because the mean of its divisors is an integer number (780560829).

Almost surely, 2^1561121657 is an apocalyptic number.

It is an amenable number.

1561121657 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561121657 is an equidigital number, since it uses as much as digits as its factorization.

1561121657 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 12600, while the sum is 35.

The square root of 1561121657 is about 39511.0320923157. The cubic root of 1561121657 is about 1160.0558972767.

The spelling of 1561121657 in words is "one billion, five hundred sixty-one million, one hundred twenty-one thousand, six hundred fifty-seven".