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 A048889 Composite numbers not ending in zero that yield a prime when turned upside down. 2
 68, 116, 118, 161, 166, 169, 188, 608, 616, 1006, 1018, 1066, 1081, 1096, 1106, 1108, 1118, 1169, 1186, 1606, 1618, 1808, 1816, 1898, 1916, 1918, 1969, 1981, 1988, 1996, 6001, 6008, 6016, 6098, 6188, 6191, 6196, 6616, 6668, 6698, 6808, 6809, 6881, 6896 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel and Reinhard Zumkeller, Table of n, a(n) for n = 1..10000 (a(1) to a(1048) from Reinhard Zumkeller) EXAMPLE 68 is not prime, yet when turned upside down gives 89 which is prime. MAPLE N:= 1000: # to get a(1) to a(N) count:= 0: for q from 1 while count < N do   if q mod 5 <> 0 then     L:= convert(q, base, 5);     m:= nops(L);     Lx:= subs(2=6, 3=8, 4=9, L);     x:= add(Lx[i]*10^(i-1), i=1..m);     if isprime(x) then next fi;     Ly:= subs(2=9, 3=8, 4=6, L);     y:= add(Ly[-i]*10^(i-1), i=1..m);     if isprime(y) then       count:= count+1;       A[count]:= x;     fi fi od: seq(A[i], i=1..count); # Robert Israel, Jul 11 2016 PROG (Haskell) import Data.List (intersect) import Numeric (readInt) import Data.Char (digitToInt) a048889 n = a048889_list !! (n-1) a048889_list = filter f a002808_list where    f n = n `mod` 10 > 0 &&          null ("23547" `intersect` show n)  &&          (a010051 (fst \$ head \$ readInt 10 (const True) ud \$ ns) == 1)        where ns = reverse \$ show n              ud '6' = 9              ud '9' = 6              ud z = digitToInt z -- Reinhard Zumkeller, Aug 11 2011 CROSSREFS Cf. A002808, A010051. Sequence in context: A039540 A235284 A250765 * A111379 A044191 A044572 Adjacent sequences:  A048886 A048887 A048888 * A048890 A048891 A048892 KEYWORD base,easy,nonn,nice AUTHOR STATUS approved

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Last modified October 15 10:15 EDT 2019. Contains 328026 sequences. (Running on oeis4.)