61491981 has 4 divisors (see below), whose sum is σ = 81989312. Its totient is φ = 40994652.

The previous prime is 61491973. The next prime is 61492051. The reversal of 61491981 is 18919416.

61491981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

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.

It is not a de Polignac number, because 61491981 - 2³ = 61491973 is a prime.

It is a super-2 number, since 2×61491981² = 7562527454608722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (61491901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10248661 + ... + 10248666.

It is an arithmetic number, because the mean of its divisors is an integer number (20497328).

Almost surely, 2^61491981 is an apocalyptic number.

It is an amenable number.

61491981 is a deficient number, since it is larger than the sum of its proper divisors (20497331).

61491981 is a wasteful number, since it uses less digits than its factorization.

61491981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20497330.

The product of its digits is 15552, while the sum is 39.

The square root of 61491981 is about 7841.6822812455. The cubic root of 61491981 is about 394.7051819220.

The spelling of 61491981 in words is "sixty-one million, four hundred ninety-one thousand, nine hundred eighty-one".