66988921 has 2 divisors, whose sum is σ = 66988922. Its totient is φ = 66988920.

The previous prime is 66988871. The next prime is 66988931. The reversal of 66988921 is 12988966.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 54464400 + 12524521 = 7380^2 + 3539^2 .

It is a cyclic number.

It is not a de Polignac number, because 66988921 - 2¹⁹ = 66464633 is a prime.

It is not a weakly prime, because it can be changed into another prime (66988931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33494460 + 33494461.

It is an arithmetic number, because the mean of its divisors is an integer number (33494461).

Almost surely, 2^66988921 is an apocalyptic number.

It is an amenable number.

66988921 is a deficient number, since it is larger than the sum of its proper divisors (1).

66988921 is an equidigital number, since it uses as much as digits as its factorization.

66988921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 373248, while the sum is 49.

The square root of 66988921 is about 8184.6759862563. The cubic root of 66988921 is about 406.1324217998.

The spelling of 66988921 in words is "sixty-six million, nine hundred eighty-eight thousand, nine hundred twenty-one".