21891437 has 2 divisors, whose sum is σ = 21891438. Its totient is φ = 21891436.

The previous prime is 21891431. The next prime is 21891449. The reversal of 21891437 is 73419812.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11464996 + 10426441 = 3386^2 + 3229^2 .

It is a cyclic number.

It is not a de Polignac number, because 21891437 - 2⁴ = 21891421 is a prime.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 21891397 and 21891406.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21891431) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10945718 + 10945719.

It is an arithmetic number, because the mean of its divisors is an integer number (10945719).

Almost surely, 2^21891437 is an apocalyptic number.

It is an amenable number.

21891437 is a deficient number, since it is larger than the sum of its proper divisors (1).

21891437 is an equidigital number, since it uses as much as digits as its factorization.

21891437 is an evil number, because the sum of its binary digits is even.

The product of its digits is 12096, while the sum is 35.

The square root of 21891437 is about 4678.8285927142. The cubic root of 21891437 is about 279.7422670879.

The spelling of 21891437 in words is "twenty-one million, eight hundred ninety-one thousand, four hundred thirty-seven".