6651721511 has 4 divisors (see below), whose sum is σ = 6651928752. Its totient is φ = 6651514272.

The previous prime is 6651721507. The next prime is 6651721519. The reversal of 6651721511 is 1151271566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1151271566 = 2 ⋅575635783.

It is a cyclic number.

It is not a de Polignac number, because 6651721511 - 2² = 6651721507 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6651721519) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 44066 + ... + 123471.

It is an arithmetic number, because the mean of its divisors is an integer number (1662982188).

Almost surely, 2^6651721511 is an apocalyptic number.

6651721511 is a deficient number, since it is larger than the sum of its proper divisors (207241).

6651721511 is a wasteful number, since it uses less digits than its factorization.

6651721511 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 207240.

The product of its digits is 12600, while the sum is 35.

The square root of 6651721511 is about 81558.0867296432. The cubic root of 6651721511 is about 1880.6646125192.

The spelling of 6651721511 in words is "six billion, six hundred fifty-one million, seven hundred twenty-one thousand, five hundred eleven".