1281016721 has 2 divisors, whose sum is σ = 1281016722. Its totient is φ = 1281016720.

The previous prime is 1281016699. The next prime is 1281016747. The reversal of 1281016721 is 1276101821.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 954130321 + 326886400 = 30889^2 + 18080^2 .

It is a cyclic number.

It is not a de Polignac number, because 1281016721 - 2¹⁸ = 1280754577 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (1281016421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 640508360 + 640508361.

It is an arithmetic number, because the mean of its divisors is an integer number (640508361).

Almost surely, 2^1281016721 is an apocalyptic number.

It is an amenable number.

1281016721 is a deficient number, since it is larger than the sum of its proper divisors (1).

1281016721 is an equidigital number, since it uses as much as digits as its factorization.

1281016721 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1344, while the sum is 29.

The square root of 1281016721 is about 35791.2939274344. The cubic root of 1281016721 is about 1086.0544502837.

The spelling of 1281016721 in words is "one billion, two hundred eighty-one million, sixteen thousand, seven hundred twenty-one".