21770681 has 2 divisors, whose sum is σ = 21770682. Its totient is φ = 21770680.

The previous prime is 21770657. The next prime is 21770687. The reversal of 21770681 is 18607712.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21529600 + 241081 = 4640^2 + 491^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21770681 is a prime.

It is a super-2 number, since 2×21770681² = 947925102407522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (21770687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10885340 + 10885341.

It is an arithmetic number, because the mean of its divisors is an integer number (10885341).

Almost surely, 2^21770681 is an apocalyptic number.

It is an amenable number.

21770681 is a deficient number, since it is larger than the sum of its proper divisors (1).

21770681 is an equidigital number, since it uses as much as digits as its factorization.

21770681 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 4704, while the sum is 32.

The square root of 21770681 is about 4665.9062356631. The cubic root of 21770681 is about 279.2269535600.

The spelling of 21770681 in words is "twenty-one million, seven hundred seventy thousand, six hundred eighty-one".