8999

This number is a prime.

A prime number whose sum of digits (sod) is greater than or equal to the near-repdigit prime 8999 must be titanic.

The smallest prime numbers whose sum of digits equals the n-th prime:    

   1 -> sod(2)=2 [Honaker]
   2 -> sod(3)=3 [Honaker]
   3 -> sod(5)=5 [Honaker]
   4 -> sod(7)=7 [Honaker]
   5 -> sod(29)=11 [Honaker]
   6 -> sod(67)=13 [Honaker]
   7 -> sod(89)=17 [Honaker]
   8 -> sod(199)=19 [Honaker]
   9 -> sod(599)=23 [Honaker]
  10 -> sod(2999)=29 [Honaker]
  11 -> sod(4999)=31 [Honaker]
  12 -> sod(29989)=37 [Chua]
  13 -> sod(59999)=41 [Chua]
  14 -> sod(79999)=43 [Chua]
  15 -> sod(389999)=47 [Chua]
  16 -> sod(989999)=53 [Chua]
  17 -> sod(6999899)=59 [Chua]
  18 -> sod(8989999)=61 [Chua]
  19 -> sod(59899999)=67 [Chua]
  20 -> sod(89999999)=71 [Chua]
  21 -> sod(289999999)=73 [Chua]
  22 -> sod(799999999)=79 [Chua]
  23 -> sod(3999998999)=83 [Chua]   
  24 -> sod(18989999999)=89 [Gaydos]
  25 -> sod(79999999999)=97 [Marcus]  
  26 -> sod(399999998999)=101 [Marcus]
  27 -> sod(599999899999)=103 [Marcus]
  28 -> sod(999998999999)=107 [Wilson]
  29 -> sod(2999998999999)=109 [Luhn]
  30 -> sod(6999998999999)=113 [Gaydos]
  31 -> sod(299999989999999)=127 [Gaydos]
  32 -> sod(789989999999999)=131 [Gaydos]
  33 -> sod(3999999999999989)=137 [Gaydos] 
  34 -> sod(5999999999899999)=139 [Gaydos]
  35 -> sod(69989999999999999)=149 [Gaydos]
  36 -> sod(89989999999999999)=151 [Gaydos]
  37 -> sod(599999999999899999)=157 [Rivera]
  38 -> sod(2999998999999999999)=163 [Rivera]
  39 -> sod(7799999999999999999)=167 [Gaydos]
  40 -> sod(29999999999999999999)=173 [Bajpai]
  41 -> sod(89999999999999999999)=179 [Bajpai]
  42 -> sod(299999899999999999999)=181 [Gupta]
  43 -> sod(4799999999999999999999)=191 [Gupta] 
  44 -> sod(5899999999999999999999)=193 [Gupta]
  45 -> sod(9998999999999999999999)=197 [Bajpai]
  46 -> sod(29998999999999999999999)=199 [Gaydos]
  47 -> sod(599999999999899999999999)=211 [Gupta] 
  48 -> sod(17989999999999999999999999)=223 [Gaydos]
  49 -> sod(39998999999999999999999999)=227 [Gupta]
  50 -> sod(59999999999899999999999999)=229 [Gupta]
  51 -> sod(99999999999999998999999999)=233 [Rivera]
  52 -> sod(698999999999999999999999999)=239 [Gupta]
  53 -> sod(899999998999999999999999999)=241 [Gupta]
  54 -> sod(18899999999999999999999999999)=251 [Gupta]
  55 -> sod(59999999999999999999999999999)=257 [Gupta]
  56 -> sod(489999999899999999999999999999)=263 [Gaydos]
  57 -> sod(899999999999999999999999999999)=269 [Gupta]
  58 -> sod(2999999999999999999999989999999)=271 [Gupta]
  59 -> sod(8999899999999999999999999999999)=277 [Gupta]
   .
   .
   .
1117 -> sod(see number)=8999. [Bajpai]

(8999, 9001) is the only case of twin primes less than a googol of form (9*10^n-1, 9*10^n+1). [Loungrides]

Warning: Do not subtract the prime number 8999 from its reversal and turn the difference upside down. [Heath]

The largest four-digit near-repdigit prime is the reversal of the largest four-digit semiprime. [Silva]

8999 followed by seventy-two 3's is a prime whose sum of digits equals the prime 251. [Bajpai]