21967661 has 2 divisors, whose sum is σ = 21967662. Its totient is φ = 21967660.

The previous prime is 21967657. The next prime is 21967663. The reversal of 21967661 is 16676912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21799561 + 168100 = 4669^2 + 410^2 .

It is a cyclic number.

It is not a de Polignac number, because 21967661 - 2² = 21967657 is a prime.

It is a super-3 number, since 3×21967661³ (a number of 23 digits) contains 333 as substring.

Together with 21967663, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21967663) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10983830 + 10983831.

It is an arithmetic number, because the mean of its divisors is an integer number (10983831).

Almost surely, 2^21967661 is an apocalyptic number.

It is an amenable number.

21967661 is a deficient number, since it is larger than the sum of its proper divisors (1).

21967661 is an equidigital number, since it uses as much as digits as its factorization.

21967661 is an evil number, because the sum of its binary digits is even.

The product of its digits is 27216, while the sum is 38.

The square root of 21967661 is about 4686.9671430468. The cubic root of 21967661 is about 280.0665700561.

The spelling of 21967661 in words is "twenty-one million, nine hundred sixty-seven thousand, six hundred sixty-one".