1561505021 has 2 divisors, whose sum is σ = 1561505022. Its totient is φ = 1561505020.

The previous prime is 1561504939. The next prime is 1561505083. The reversal of 1561505021 is 1205051651.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1296792121 + 264712900 = 36011^2 + 16270^2 .

It is a cyclic number.

It is not a de Polignac number, because 1561505021 - 2¹⁰ = 1561503997 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1561505221) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780752510 + 780752511.

It is an arithmetic number, because the mean of its divisors is an integer number (780752511).

Almost surely, 2^1561505021 is an apocalyptic number.

It is an amenable number.

1561505021 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561505021 is an equidigital number, since it uses as much as digits as its factorization.

1561505021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1500, while the sum is 26.

The square root of 1561505021 is about 39515.8831484253. The cubic root of 1561505021 is about 1160.1508476539.

Adding to 1561505021 its reverse (1205051651), we get a palindrome (2766556672).

The spelling of 1561505021 in words is "one billion, five hundred sixty-one million, five hundred five thousand, twenty-one".