209986501609921 has 9 divisors (see below), whose sum is σ = 210341823915171. Its totient is φ = 209631778599552.

The previous prime is 209986501609883. The next prime is 209986501609931. The reversal of 209986501609921 is 129906105689902.

The square root of 209986501609921 is 14490911.

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., 25904995193025 + 184081506416896 = 5089695^2 + 13567664^2 .

It is a de Polignac number, because none of the positive numbers 2^k-209986501609921 is a prime.

It is a super-3 number, since 3×209986501609921³ (a number of 44 digits) contains 333 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (209986501609931) by changing a digit.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 8795971041 + ... + 8795994913.

Almost surely, 2^{209986501609921} is an apocalyptic number.

209986501609921 is the 14490911-st square number.

209986501609921 is the 7245456-th centered octagonal number.

It is an amenable number.

209986501609921 is a deficient number, since it is larger than the sum of its proper divisors (355322305250).

209986501609921 is an frugal number, since it uses more digits than its factorization.

209986501609921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48960 (or 24480 counting only the distinct ones).

The product of its (nonzero) digits is 37791360, while the sum is 67.

The spelling of 209986501609921 in words is "two hundred nine trillion, nine hundred eighty-six billion, five hundred one million, six hundred nine thousand, nine hundred twenty-one".