A105581 Primes whose indices are palindromic.
2, 3, 5, 7, 11, 13, 17, 19, 23, 31, 79, 137, 193, 257, 317, 389, 457, 523, 547, 607, 661, 739, 811, 877, 947, 1019, 1087, 1153, 1231, 1301, 1399, 1459, 1531, 1601, 1667, 1747, 1831, 1907, 1999, 2081, 2141, 2239, 2309, 2381, 2447, 2549, 2647, 2699, 2777, 2851
Offset: 1
Examples
prime(22) = 79 prime(33) = 137 the 11th and 12th entries.
Crossrefs
Cf. A258433.
Programs
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Mathematica
Prime[#]&/@Select[Range[500],PalindromeQ] (* Harvey P. Dale, Nov 24 2022 *)
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PARI
g(n) = for(x=1,n,if(ispal(x),print1(prime(x)","))) ispal(n) = { local(len,s1,s2); n=Str(n); len=length(n)\2; s1 = left(n,len); s2 = right(n,len); if(s1 == rev(s2),return(1),return(0)) } left(str,n) = \ Get the left n characters from string str. { local(v,tmp,x); v =""; tmp = Vec(str); ln=length(tmp); if(n > ln,n=ln); for(x=1,n, v=concat(v,tmp[x]); ); return(v) } right(str,n) = \ Get the right n characters from string str. { local(v,ln,s,x); v =""; tmp = Vec(str); ln=length(tmp); if(n > ln,n=ln); s = ln-n+1; for(x=s,ln, v=concat(v,tmp[x]); ); return(v) } rev(str) = \ Get the reverse of the input string { local(tmp,s,j); tmp = Vec(Str(str)); s=""; forstep(j=length(tmp),1,-1, s=concat(s,tmp[j])); return(s) }