681279721 has 2 divisors, whose sum is σ = 681279722. Its totient is φ = 681279720.

The previous prime is 681279707. The next prime is 681279737. The reversal of 681279721 is 127972186.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 446730496 + 234549225 = 21136^2 + 15315^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-681279721 is a prime.

It is not a weakly prime, because it can be changed into another prime (681279701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 340639860 + 340639861.

It is an arithmetic number, because the mean of its divisors is an integer number (340639861).

Almost surely, 2^681279721 is an apocalyptic number.

It is an amenable number.

681279721 is a deficient number, since it is larger than the sum of its proper divisors (1).

681279721 is an equidigital number, since it uses as much as digits as its factorization.

681279721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 84672, while the sum is 43.

The square root of 681279721 is about 26101.3356171672. The cubic root of 681279721 is about 879.9172274936.

It can be divided in two parts, 68 and 1279721, that multiplied together give a triangular number (87021028 = T₁₃₁₉₂).

The spelling of 681279721 in words is "six hundred eighty-one million, two hundred seventy-nine thousand, seven hundred twenty-one".