21617381 has 2 divisors, whose sum is σ = 21617382. Its totient is φ = 21617380.

The previous prime is 21617377. The next prime is 21617411. The reversal of 21617381 is 18371612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 16532356 + 5085025 = 4066^2 + 2255^2 .

It is a cyclic number.

It is not a de Polignac number, because 21617381 - 2² = 21617377 is a prime.

It is a super-2 number, since 2×21617381² = 934622322598322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21617341) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10808690 + 10808691.

It is an arithmetic number, because the mean of its divisors is an integer number (10808691).

Almost surely, 2^21617381 is an apocalyptic number.

It is an amenable number.

21617381 is a deficient number, since it is larger than the sum of its proper divisors (1).

21617381 is an equidigital number, since it uses as much as digits as its factorization.

21617381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2016, while the sum is 29.

The square root of 21617381 is about 4649.4495373108. The cubic root of 21617381 is about 278.5700094853.

Adding to 21617381 its reverse (18371612), we get a palindrome (39988993).

The spelling of 21617381 in words is "twenty-one million, six hundred seventeen thousand, three hundred eighty-one".