9917968921 has 27 divisors (see below), whose sum is σ = 11859665727. Its totient is φ = 8269870560.

The previous prime is 9917968919. The next prime is 9917968927. The reversal of 9917968921 is 1298697199.

The square root of 9917968921 is 99589.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 477903321 + 9440065600 = 21861^2 + 97160^2 .

It is not a de Polignac number, because 9917968921 - 2¹ = 9917968919 is a prime.

It is a super-2 number, since 2×9917968921² (a number of 21 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 9917968921.

It is not an unprimeable number, because it can be changed into a prime (9917968927) by changing a digit.

It is a polite number, since it can be written in 26 ways as a sum of consecutive naturals, for example, 28581870 + ... + 28582216.

Almost surely, 2^9917968921 is an apocalyptic number.

9917968921 is the 99589-th square number.

9917968921 is the 49795-th centered octagonal number.

It is an amenable number.

9917968921 is a deficient number, since it is larger than the sum of its proper divisors (1941696806).

9917968921 is an frugal number, since it uses more digits than its factorization.

9917968921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 790 (or 395 counting only the distinct ones).

The product of its digits is 4408992, while the sum is 61.

The cubic root of 9917968921 is about 2148.5274879186.

It can be divided in two parts, 99179 and 68921, that added together give a square (168100 = 410²).

The spelling of 9917968921 in words is "nine billion, nine hundred seventeen million, nine hundred sixty-eight thousand, nine hundred twenty-one".