61721440181 has 2 divisors, whose sum is σ = 61721440182. Its totient is φ = 61721440180.

The previous prime is 61721440117. The next prime is 61721440211. The reversal of 61721440181 is 18104412716.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 61578422500 + 143017681 = 248150^2 + 11959^2 .

It is a cyclic number.

It is not a de Polignac number, because 61721440181 - 2⁶ = 61721440117 is a prime.

It is a super-2 number, since 2×61721440181² (a number of 22 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (61721440111) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 30860720090 + 30860720091.

It is an arithmetic number, because the mean of its divisors is an integer number (30860720091).

Almost surely, 2^61721440181 is an apocalyptic number.

It is an amenable number.

61721440181 is a deficient number, since it is larger than the sum of its proper divisors (1).

61721440181 is an equidigital number, since it uses as much as digits as its factorization.

61721440181 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10752, while the sum is 35.

Adding to 61721440181 its reverse (18104412716), we get a palindrome (79825852897).

The spelling of 61721440181 in words is "sixty-one billion, seven hundred twenty-one million, four hundred forty thousand, one hundred eighty-one".