6461881681 has 2 divisors, whose sum is σ = 6461881682. Its totient is φ = 6461881680.

The previous prime is 6461881597. The next prime is 6461881691. The reversal of 6461881681 is 1861881646.

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., 3996262656 + 2465619025 = 63216^2 + 49655^2 .

It is a cyclic number.

It is not a de Polignac number, because 6461881681 - 2¹³ = 6461873489 is a prime.

It is a super-2 number, since 2×6461881681² = 83511829718486771522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (6461881691) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3230940840 + 3230940841.

It is an arithmetic number, because the mean of its divisors is an integer number (3230940841).

Almost surely, 2^6461881681 is an apocalyptic number.

It is an amenable number.

6461881681 is a deficient number, since it is larger than the sum of its proper divisors (1).

6461881681 is an equidigital number, since it uses as much as digits as its factorization.

6461881681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 442368, while the sum is 49.

The square root of 6461881681 is about 80385.8301008331. The cubic root of 6461881681 is about 1862.6002942613.

The spelling of 6461881681 in words is "six billion, four hundred sixty-one million, eight hundred eighty-one thousand, six hundred eighty-one".