1561020521 has 2 divisors, whose sum is σ = 1561020522. Its totient is φ = 1561020520.

The previous prime is 1561020509. The next prime is 1561020523. The reversal of 1561020521 is 1250201651.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 934219225 + 626801296 = 30565^2 + 25036^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1561020521 is a prime.

It is a super-2 number, since 2×1561020521² = 4873570133966222882, which contains 22 as substring.

Together with 1561020523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (1561020523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 780510260 + 780510261.

It is an arithmetic number, because the mean of its divisors is an integer number (780510261).

Almost surely, 2^1561020521 is an apocalyptic number.

It is an amenable number.

1561020521 is a deficient number, since it is larger than the sum of its proper divisors (1).

1561020521 is an equidigital number, since it uses as much as digits as its factorization.

1561020521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 600, while the sum is 23.

The square root of 1561020521 is about 39509.7522265073. The cubic root of 1561020521 is about 1160.0308456423.

The spelling of 1561020521 in words is "one billion, five hundred sixty-one million, twenty thousand, five hundred twenty-one".