42661981 has 2 divisors, whose sum is σ = 42661982. Its totient is φ = 42661980.

The previous prime is 42661963. The next prime is 42662021. The reversal of 42661981 is 18916624.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 41396356 + 1265625 = 6434^2 + 1125^2 .

It is a cyclic number.

It is not a de Polignac number, because 42661981 - 2⁹ = 42661469 is a prime.

It is a super-2 number, since 2×42661981² = 3640089245688722, which contains 22 as substring.

It is equal to p_2585395 and since 42661981 and 2585395 have the same sum of digits, it is a Honaker prime.

It is a self number, because there is not a number n which added to its sum of digits gives 42661981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (42661961) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 21330990 + 21330991.

It is an arithmetic number, because the mean of its divisors is an integer number (21330991).

Almost surely, 2^42661981 is an apocalyptic number.

It is an amenable number.

42661981 is a deficient number, since it is larger than the sum of its proper divisors (1).

42661981 is an equidigital number, since it uses as much as digits as its factorization.

42661981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 20736, while the sum is 37.

The square root of 42661981 is about 6531.6139659352. The cubic root of 42661981 is about 349.4193938423.

The spelling of 42661981 in words is "forty-two million, six hundred sixty-one thousand, nine hundred eighty-one".