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 A090261 Beginning with a(1) = 1, choose a(n+1) so that concatenation a(n+1), a(n), a(n+1) is a new prime. 2
 1, 3, 1, 9, 1, 17, 1, 21, 11, 13, 17, 7, 3, 11, 19, 9, 7, 111, 17, 13, 23, 1, 27, 17, 37, 3, 13, 33, 23, 7, 129, 11, 27, 43, 3, 17, 39, 17, 103, 3, 19, 17, 121, 117, 1, 29, 1, 39, 23, 9, 13, 51, 1, 41, 3, 37, 21, 13, 53, 1, 47, 1, 51, 7, 131, 7, 137, 19, 23, 13, 71, 7, 149, 1, 59, 3 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS H. v. Eitzen, Table of n, a(n) for n = 1..10000. EXAMPLE 313, 131, 919, 191, 17117, 1171, 21121, etc. are primes. PROG (PARI) tp(n)=10^ceil(log(n+0.5)/log(10)); seen=Set([]); a=[1]; while(#a<100, n=a[ #a]; tn=tp(n); k=1; while(!isprime(z=(k*tn+n)*tp(k)+k) || setsearch(seen, z), k+=2); seen=setunion(seen, [z]); a=concat(a, k)); a \\ Hagen von Eitzen, Jun 21 2009 CROSSREFS Cf. A090260. Sequence in context: A197259 A200006 A070894 * A303552 A130599 A157674 Adjacent sequences:  A090258 A090259 A090260 * A090262 A090263 A090264 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 28 2003 EXTENSIONS a(14) corrected and more terms added by Hagen von Eitzen, Jun 21 2009 STATUS approved

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Last modified November 29 11:56 EST 2020. Contains 338766 sequences. (Running on oeis4.)