67721981 has 2 divisors, whose sum is σ = 67721982. Its totient is φ = 67721980.

The previous prime is 67721957. The next prime is 67722013. The reversal of 67721981 is 18912776.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 50993881 + 16728100 = 7141^2 + 4090^2 .

It is a cyclic number.

It is not a de Polignac number, because 67721981 - 2¹⁸ = 67459837 is a prime.

It is a super-2 number, since 2×67721981² = 9172533421128722, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (67721921) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33860990 + 33860991.

It is an arithmetic number, because the mean of its divisors is an integer number (33860991).

Almost surely, 2^67721981 is an apocalyptic number.

It is an amenable number.

67721981 is a deficient number, since it is larger than the sum of its proper divisors (1).

67721981 is an equidigital number, since it uses as much as digits as its factorization.

67721981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 42336, while the sum is 41.

The square root of 67721981 is about 8229.3366075280. The cubic root of 67721981 is about 407.6084868042.

The spelling of 67721981 in words is "sixty-seven million, seven hundred twenty-one thousand, nine hundred eighty-one".