821 = prime number, twin prime, Eisenstein prime with no imaginary part, prime quadruplet with 823, 827, 829
822 = 2 × 3 × 137, sum of twelve consecutive primes (43 + 47 + 53 + 59 + 61 + 67 + 71 + 73 + 79 + 83 + 89 + 97), sphenic number, member of the Mian–Chowla sequence[9]
823 = prime number, twin prime, the Mertens function of 823 returns 0, prime quadruplet with 821, 827, 829
824 = 23 × 103, sum of ten consecutive primes (61 + 67 + 71 + 73 + 79 + 83 + 89 + 97 + 101 + 103), the Mertens function of 824 returns 0, nontotient
825 = 3 × 52 × 11, Smith number,[10] the Mertens function of 825 returns 0, Harshad number
826 = 2 × 7 × 59, sphenic number
827 = prime number, twin prime, part of prime quadruplet with {821, 823, 829}, sum of seven consecutive primes (103 + 107 + 109 + 113 + 127 + 131 + 137), Chen prime, Eisenstein prime with no imaginary part, strictly non-palindromic number[11]
828 = 22 × 32 × 23, Harshad number
829 = prime number, twin prime, part of prime quadruplet with {827, 823, 821}, sum of three consecutive primes (271 + 277 + 281), Chen prime
830s
830 = 2 × 5 × 83, sphenic number, sum of four consecutive primes (197 + 199 + 211 + 223), nontotient, totient sum for first 52 integers
831 = 3 × 277
832 = 26 × 13, Harshad number
833 = 72 × 17
834 = 2 × 3 × 139, sphenic number, sum of six consecutive primes (127 + 131 + 137 + 139 + 149 + 151), nontotient
839 = prime number, safe prime,[13] sum of five consecutive primes (157 + 163 + 167 + 173 + 179), Chen prime, Eisenstein prime with no imaginary part, highly cototient number[14]
840s
840 = 23 × 3 × 5 × 7, highly composite number,[15] smallest numbers divisible by the numbers 1 to 8 (lowest common multiple of 1 to 8), sparsely totient number,[16] Harshad number in base 2 through base 10
849 = 3 × 283, the Mertens function of 849 returns 0
850s
850 = 2 × 52 × 17, the Mertens function of 850 returns 0, nontotient, the maximum possible Fair Isaac credit score, country calling code for North Korea
853 = prime number, Perrin number,[22] the Mertens function of 853 returns 0, average of first 853 prime numbers is an integer (sequence A045345 in the OEIS), strictly non-palindromic number, number of connected graphs with 7 nodes
863 = prime number, safe prime,[13] sum of five consecutive primes (163 + 167 + 173 + 179 + 181), sum of seven consecutive primes (107 + 109 + 113 + 127 + 131 + 137 + 139), Chen prime, Eisenstein prime with no imaginary part
864 = 25 × 33, sum of a twin prime (431 + 433), sum of six consecutive primes (131 + 137 + 139 + 149 + 151 + 157), Harshad number
865 = 5 × 173,
866 = 2 × 433, nontotient
867 = 3 × 172
868 = 22 × 7 × 31, nontotient
869 = 11 × 79, the Mertens function of 869 returns 0
881 = prime number, twin prime, sum of nine consecutive primes (79 + 83 + 89 + 97 + 101 + 103 + 107 + 109 + 113), Chen prime, Eisenstein prime with no imaginary part, happy number
882 = 2 × 32 × 72, Harshad number, totient sum for first 53 integers
883 = prime number, twin prime, sum of three consecutive primes (283 + 293 + 307), the Mertens function of 883 returns 0
884 = 22 × 13 × 17, the Mertens function of 884 returns 0
885 = 3 × 5 × 59, sphenic number
886 = 2 × 443, the Mertens function of 886 returns 0
country calling code for Taiwan
887 = prime number followed by primal gap of 20, safe prime,[13] Chen prime, Eisenstein prime with no imaginary part