21984397 has 2 divisors, whose sum is σ = 21984398. Its totient is φ = 21984396.

The previous prime is 21984359. The next prime is 21984421. The reversal of 21984397 is 79348912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20529961 + 1454436 = 4531^2 + 1206^2 .

It is a cyclic number.

It is not a de Polignac number, because 21984397 - 2²³ = 13595789 is a prime.

It is a super-2 number, since 2×21984397² = 966627422907218, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21984307) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10992198 + 10992199.

It is an arithmetic number, because the mean of its divisors is an integer number (10992199).

Almost surely, 2^21984397 is an apocalyptic number.

It is an amenable number.

21984397 is a deficient number, since it is larger than the sum of its proper divisors (1).

21984397 is an equidigital number, since it uses as much as digits as its factorization.

21984397 is an evil number, because the sum of its binary digits is even.

The product of its digits is 108864, while the sum is 43.

The square root of 21984397 is about 4688.7521794183. The cubic root of 21984397 is about 280.1376746419.

It can be divided in two parts, 2198 and 4397, that multiplied together give a triangular number (9664606 = T₄₃₉₆).

The spelling of 21984397 in words is "twenty-one million, nine hundred eighty-four thousand, three hundred ninety-seven".