1291668721 has 16 divisors (see below), whose sum is σ = 1564617600. Its totient is φ = 1040958720.

The previous prime is 1291668629. The next prime is 1291668727. The reversal of 1291668721 is 1278661921.

It is a cyclic number.

It is not a de Polignac number, because 1291668721 - 2⁷ = 1291668593 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1291668727) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 124855 + ... + 134803.

It is an arithmetic number, because the mean of its divisors is an integer number (97788600).

Almost surely, 2^1291668721 is an apocalyptic number.

It is an amenable number.

1291668721 is a deficient number, since it is larger than the sum of its proper divisors (272948879).

1291668721 is a wasteful number, since it uses less digits than its factorization.

1291668721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11064.

The product of its digits is 72576, while the sum is 43.

The square root of 1291668721 is about 35939.7930016298. The cubic root of 1291668721 is about 1089.0564235445.

The spelling of 1291668721 in words is "one billion, two hundred ninety-one million, six hundred sixty-eight thousand, seven hundred twenty-one".