21378817 has 2 divisors, whose sum is σ = 21378818. Its totient is φ = 21378816.

The previous prime is 21378767. The next prime is 21378883. The reversal of 21378817 is 71887312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15023376 + 6355441 = 3876^2 + 2521^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21378817 is a prime.

It is not a weakly prime, because it can be changed into another prime (21378317) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10689408 + 10689409.

It is an arithmetic number, because the mean of its divisors is an integer number (10689409).

Almost surely, 2^21378817 is an apocalyptic number.

It is an amenable number.

21378817 is a deficient number, since it is larger than the sum of its proper divisors (1).

21378817 is an equidigital number, since it uses as much as digits as its factorization.

21378817 is an evil number, because the sum of its binary digits is even.

The product of its digits is 18816, while the sum is 37.

The square root of 21378817 is about 4623.7232832426. The cubic root of 21378817 is about 277.5414736595.

The spelling of 21378817 in words is "twenty-one million, three hundred seventy-eight thousand, eight hundred seventeen".