61781 has 2 divisors, whose sum is σ = 61782. Its totient is φ = 61780.

The previous prime is 61757. The next prime is 61813. The reversal of 61781 is 18716.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 34225 + 27556 = 185^2 + 166^2 .

It is a cyclic number.

It is not a de Polignac number, because 61781 - 2⁶ = 61717 is a prime.

It is a super-2 number, since 2×61781² = 7633783922, which contains 22 as substring.

It is a Chen prime.

It is an Ulam number.

It is a plaindrome in base 15.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (61751) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 30890 + 30891.

It is an arithmetic number, because the mean of its divisors is an integer number (30891).

2⁶¹⁷⁸¹ is an apocalyptic number.

It is an amenable number.

61781 is a deficient number, since it is larger than the sum of its proper divisors (1).

61781 is an equidigital number, since it uses as much as digits as its factorization.

61781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 336, while the sum is 23.

The square root of 61781 is about 248.5578403511. The cubic root of 61781 is about 39.5322601381.

The spelling of 61781 in words is "sixty-one thousand, seven hundred eighty-one".