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 A176356 Numbers which when seen in a mirror are primes (or 1), using calculator-style 7-segment numerals. 0
 1, 2, 5, 10, 11, 20, 50, 100, 101, 110, 115, 118, 121, 125, 152, 158, 181, 185, 188, 200, 500, 1000, 1010, 1012, 1018, 1022, 1028, 1051, 1081, 1082, 1085, 1100, 1102, 1105, 1108, 1115, 1118, 1121, 1150, 1180, 1181, 1201, 1202, 1210, 1211, 1225, 1250, 1255, 1282, 1285, 1501, 1502, 1520, 1522 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS We construct mirror images of numbers by placing a mirror parallel to the baseline at an acute angle and looking at them from the top of the sheet they are written on. This defines the mirror images by fixing digits 0, 1 and 8, exchanging 2 and 5, reversing the order of the digits and ignoring leading zeros that may result. Only entries of A080228 are admitted, because 3's, 4's, 6's, 7's and 9's do not have calculator style images. If this combined operation on n generates an entry in A008578, n is in this sequence here. REFERENCES P. Giannopoulos, The Brainteasers, unpublished. LINKS EXAMPLE 110 is in the sequence because the mirror is 011 = 11 and prime. 152 is in the sequence because the mirror is 521 = A000040(98), a prime. 31 is not in the sequence because the 3 cannot be mirrored. 115 is in the sequence because the mirror is 211 = A000040(47), a prime. MAPLE calcmirr := proc(n)         local L, Lm, i ;         L := convert(n, base, 10) ;         Lm := [] ;         for i from 1 to nops(L) do                 if op(i, L) = 2 then                         Lm := [5, op(Lm)] ;                 elif op(i, L) = 5 then                         Lm := [2, op(Lm)] ;                 elif op(i, L) in {0, 1, 8} then                         Lm := [op(i, L), op(Lm)] ;                 else                         return 0 ;                 end if;         end do:         add(op(i, Lm)*10^(i-1), i=1..nops(Lm)) ; end proc: isA176356 := proc(n)         local m;         m := calcmirr(n) ;         isprime(m) or (m = 1) ; end proc: for n from 1 to 2001 do         if isA176356(n) then                 printf("%d, ", n);         end if; end do: # R. J. Mathar, Sep 24 2011 PROG (PARI) isa(n)=local(r, d); while(n>0, d=n%10; if(d==2, d=5, if(d==5, d=2, if(d==3||d==4||d==6||d==7||d==9, return(0)))); r=r*10+d; n\=10); isprime(r) \\ Franklin T. Adams-Watters. Produces sequence except for initial 1 CROSSREFS Cf. A080228, A080792, A008578 Sequence in context: A032874 A240032 A187792 * A196168 A018514 A018288 Adjacent sequences:  A176353 A176354 A176355 * A176357 A176358 A176359 KEYWORD base,easy,nonn AUTHOR P. Giannopoulos (pgiannop1(AT)yahoo.com), Apr 15 2010, Apr 22 2010 EXTENSIONS Sequence reconstructed with a consistent interpretation of the definition. - R. J. Mathar, Sep 24 2011 Edited by N. J. A. Sloane, Oct 24 2011 STATUS approved

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Last modified September 16 08:18 EDT 2021. Contains 347469 sequences. (Running on oeis4.)