18961381 has 2 divisors, whose sum is σ = 18961382. Its totient is φ = 18961380.

The previous prime is 18961357. The next prime is 18961403. The reversal of 18961381 is 18316981.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17297281 + 1664100 = 4159^2 + 1290^2 .

It is a cyclic number.

It is not a de Polignac number, because 18961381 - 2⁷ = 18961253 is a prime.

It is a super-2 number, since 2×18961381² = 719067938854322, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 18961381.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18961321) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9480690 + 9480691.

It is an arithmetic number, because the mean of its divisors is an integer number (9480691).

Almost surely, 2^18961381 is an apocalyptic number.

It is an amenable number.

18961381 is a deficient number, since it is larger than the sum of its proper divisors (1).

18961381 is an equidigital number, since it uses as much as digits as its factorization.

18961381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 10368, while the sum is 37.

The square root of 18961381 is about 4354.4667871049. The cubic root of 18961381 is about 266.6592510091.

The spelling of 18961381 in words is "eighteen million, nine hundred sixty-one thousand, three hundred eighty-one".