5661221681 has 2 divisors, whose sum is σ = 5661221682. Its totient is φ = 5661221680.

The previous prime is 5661221639. The next prime is 5661221719. The reversal of 5661221681 is 1861221665.

It is a happy number.

It is an a-pointer prime, because the next prime (5661221719) can be obtained adding 5661221681 to its sum of digits (38).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 4863667600 + 797554081 = 69740^2 + 28241^2 .

It is a cyclic number.

It is not a de Polignac number, because 5661221681 - 2²⁶ = 5594112817 is a prime.

It is a super-2 number, since 2×5661221681² = 64098861842848931522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (5661221611) 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, 2830610840 + 2830610841.

It is an arithmetic number, because the mean of its divisors is an integer number (2830610841).

Almost surely, 2^5661221681 is an apocalyptic number.

It is an amenable number.

5661221681 is a deficient number, since it is larger than the sum of its proper divisors (1).

5661221681 is an equidigital number, since it uses as much as digits as its factorization.

5661221681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 34560, while the sum is 38.

The square root of 5661221681 is about 75241.0903762033. The cubic root of 5661221681 is about 1782.2558698957.

The spelling of 5661221681 in words is "five billion, six hundred sixty-one million, two hundred twenty-one thousand, six hundred eighty-one".