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A105581
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Primes whose indices are palindromic.
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1
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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EXAMPLE
| prime(22) = 79 prime(33) = 137 the 11-th and 12-th entries.
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PROG
| (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) }
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CROSSREFS
| Sequence in context: A086983 A046501 A033875 * A050264 A075239 A008792
Adjacent sequences: A105578 A105579 A105580 * A105582 A105583 A105584
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KEYWORD
| easy,nonn,base
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AUTHOR
| Cino Hilliard (hillcino368(AT)gmail.com), May 03 2005
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