81666619 has 2 divisors, whose sum is σ = 81666620. Its totient is φ = 81666618.

The previous prime is 81666601. The next prime is 81666631. The reversal of 81666619 is 91666618.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 81666619 - 2¹³ = 81658427 is a prime.

It is a super-2 number, since 2×81666619² = 13338873317782322, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (81666649) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40833309 + 40833310.

It is an arithmetic number, because the mean of its divisors is an integer number (40833310).

Almost surely, 2^81666619 is an apocalyptic number.

81666619 is a deficient number, since it is larger than the sum of its proper divisors (1).

81666619 is an equidigital number, since it uses as much as digits as its factorization.

81666619 is an evil number, because the sum of its binary digits is even.

The product of its digits is 93312, while the sum is 43.

The square root of 81666619 is about 9036.9585038330. The cubic root of 81666619 is about 433.8585815582.

Subtracting 81666619 from its reverse (91666618), we obtain a palindrome (9999999).

The spelling of 81666619 in words is "eighty-one million, six hundred sixty-six thousand, six hundred nineteen".