207781900561 has 3 divisors (see below), whose sum is σ = 207782356393. Its totient is φ = 207781444730.

The previous prime is 207781900549. The next prime is 207781900583. The reversal of 207781900561 is 165009187702.

It is a happy number.

The square root of 207781900561 is 455831.

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

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is not a de Polignac number, because 207781900561 - 2¹⁵ = 207781867793 is a prime.

It is a super-2 number, since 2×207781900561² (a number of 23 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (207781900541) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 227916 + ... + 683746.

Almost surely, 2^207781900561 is an apocalyptic number.

207781900561 is the 455831-st square number.

207781900561 is the 227916-th centered octagonal number.

It is an amenable number.

207781900561 is a deficient number, since it is larger than the sum of its proper divisors (455832).

207781900561 is an frugal number, since it uses more digits than its factorization.

207781900561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 911662 (or 455831 counting only the distinct ones).

The product of its (nonzero) digits is 211680, while the sum is 46.

The spelling of 207781900561 in words is "two hundred seven billion, seven hundred eighty-one million, nine hundred thousand, five hundred sixty-one".