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A105581 Primes whose indices are palindromic. 2
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; text; internal format)
OFFSET

1,1

LINKS

Table of n, a(n) for n=1..50.

EXAMPLE

prime(22) = 79 prime(33) = 137 the 11th and 12th entries.

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) }

CROSSREFS

Cf. A258433.

Sequence in context: A219528 A046501 A033875 * A258433 A262363 A050264

Adjacent sequences:  A105578 A105579 A105580 * A105582 A105583 A105584

KEYWORD

easy,nonn,base

AUTHOR

Cino Hilliard, May 03 2005

STATUS

approved

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Last modified June 25 22:27 EDT 2019. Contains 324364 sequences. (Running on oeis4.)