121781 has 4 divisors (see below), whose sum is σ = 132864. Its totient is φ = 110700.

The previous prime is 121763. The next prime is 121787. The reversal of 121781 is 187121.

121781 = 6² + 7² + ... + 71².

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 187121 = 11 ⋅17011.

It is a cyclic number.

It is not a de Polignac number, because 121781 - 2¹⁴ = 105397 is a prime.

It is a super-2 number, since 2×121781² = 29661223922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 121781.

It is not an unprimeable number, because it can be changed into a prime (121787) 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, 5525 + ... + 5546.

It is an arithmetic number, because the mean of its divisors is an integer number (33216).

2¹²¹⁷⁸¹ is an apocalyptic number.

121781 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

121781 is a deficient number, since it is larger than the sum of its proper divisors (11083).

121781 is a wasteful number, since it uses less digits than its factorization.

121781 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11082.

The product of its digits is 112, while the sum is 20.

The square root of 121781 is about 348.9713455285. The cubic root of 121781 is about 49.5670621155.

Adding to 121781 its sum of digits (20), we get a square (121801 = 349²).

The spelling of 121781 in words is "one hundred twenty-one thousand, seven hundred eighty-one".