2521216561 has 2 divisors, whose sum is σ = 2521216562. Its totient is φ = 2521216560.

The previous prime is 2521216547. The next prime is 2521216583. The reversal of 2521216561 is 1656121252.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 2201486400 + 319730161 = 46920^2 + 17881^2 .

It is a cyclic number.

It is not a de Polignac number, because 2521216561 - 2¹¹ = 2521214513 is a prime.

It is a super-4 number, since 4×2521216561⁴ (a number of 39 digits) contains 4444 as substring.

It is an alternating number because its digits alternate between even and odd.

It is not a weakly prime, because it can be changed into another prime (2521216541) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1260608280 + 1260608281.

It is an arithmetic number, because the mean of its divisors is an integer number (1260608281).

Almost surely, 2^2521216561 is an apocalyptic number.

It is an amenable number.

2521216561 is a deficient number, since it is larger than the sum of its proper divisors (1).

2521216561 is an equidigital number, since it uses as much as digits as its factorization.

2521216561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7200, while the sum is 31.

The square root of 2521216561 is about 50211.7173675627. The cubic root of 2521216561 is about 1361.0373719057.

The spelling of 2521216561 in words is "two billion, five hundred twenty-one million, two hundred sixteen thousand, five hundred sixty-one".