A156793 Indices of primes whose reversal is a different prime.

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

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