1561121557 has 2 divisors, whose sum is σ = 1561121558. Its totient is φ = 1561121556.

The previous prime is 1561121483. The next prime is 1561121563. The reversal of 1561121557 is 7551211651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 841058001 + 720063556 = 29001^2 + 26834^2 .

It is an emirp because it is prime and its reverse (7551211651) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1561121557 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1561121657) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780560778 + 780560779.

It is an arithmetic number, because the mean of its divisors is an integer number (780560779).

Almost surely, 2^1561121557 is an apocalyptic number.

It is an amenable number.

1561121557 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561121557 is an equidigital number, since it uses as much as digits as its factorization.

1561121557 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10500, while the sum is 34.

The square root of 1561121557 is about 39511.0308268463. The cubic root of 1561121557 is about 1160.0558725070.

The spelling of 1561121557 in words is "one billion, five hundred sixty-one million, one hundred twenty-one thousand, five hundred fifty-seven".