66781921 has 2 divisors, whose sum is σ = 66781922. Its totient is φ = 66781920.

The previous prime is 66781909. The next prime is 66781927. The reversal of 66781921 is 12918766.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 66341025 + 440896 = 8145^2 + 664^2 .

It is a cyclic number.

It is not a de Polignac number, because 66781921 - 2¹¹ = 66779873 is a prime.

It is not a weakly prime, because it can be changed into another prime (66781927) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33390960 + 33390961.

It is an arithmetic number, because the mean of its divisors is an integer number (33390961).

Almost surely, 2^66781921 is an apocalyptic number.

It is an amenable number.

66781921 is a deficient number, since it is larger than the sum of its proper divisors (1).

66781921 is an equidigital number, since it uses as much as digits as its factorization.

66781921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36288, while the sum is 40.

The square root of 66781921 is about 8172.0206191615. The cubic root of 66781921 is about 405.7136652240.

The spelling of 66781921 in words is "sixty-six million, seven hundred eighty-one thousand, nine hundred twenty-one".