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 A156793 Indices of primes whose reversal is a different prime. 2
 6, 7, 11, 12, 20, 21, 22, 25, 28, 30, 35, 37, 39, 41, 46, 64, 68, 69, 72, 77, 126, 127, 130, 131, 132, 133, 135, 136, 155, 159, 160, 162, 163, 164, 166, 167, 169, 172, 173, 174, 178, 180, 182, 184, 185, 186, 190, 191, 194, 196, 197, 198, 199, 200, 201, 202, 203 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Indices of primes in A006567. LINKS Harvey P. Dale, Table of n, a(n) for n = 1..1000 EXAMPLE If prime(n=6)=13(1<3) and 31=prime, then 6=a(1). If prime(n=7)=17(1<7) and 71=prime, then 7=a(2). If prime(n=11)=31(3>1) and 13=prime, then 11=a(3), etc. MATHEMATICA difpQ[n_]:=Module[{idn=IntegerDigits[n], ridn}, ridn=Reverse[idn]; idn!=ridn && PrimeQ[FromDigits[ridn]]]; PrimePi/@ Select[ Prime[ Range[ 250]], difpQ] (* Harvey P. Dale, Nov 23 2011 *) CROSSREFS Cf. A006567. Sequence in context: A015825 A243489 A164018 * A081715 A054504 A190612 Adjacent sequences: A156790 A156791 A156792 * A156794 A156795 A156796 KEYWORD nonn,base AUTHOR Juri-Stepan Gerasimov, Feb 16 2009 EXTENSIONS 45 replaced by 46. 127, 131, 136, 155, 159 inserted, etc. - R. J. Mathar, Feb 26 2009 STATUS approved

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Last modified September 23 09:36 EDT 2023. Contains 365544 sequences. (Running on oeis4.)