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 A077202 a(1) = 1, a(n) = smallest number such that the concatenation of two successive terms gives a prime which has not occurred earlier. 2
 1, 1, 3, 1, 7, 1, 9, 7, 3, 7, 9, 11, 3, 11, 17, 3, 13, 1, 27, 1, 37, 3, 17, 9, 19, 1, 39, 7, 19, 3, 31, 19, 7, 27, 7, 33, 7, 39, 11, 23, 3, 47, 9, 29, 3, 49, 1, 49, 9, 37, 9, 41, 9, 47, 21, 1, 51, 13, 19, 9, 53, 23, 9, 67, 3, 53, 33, 13, 21, 11, 29, 17, 21, 13, 27, 11, 51, 19, 13, 61 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS Conjecture: Every odd prime occurs in this sequence infinitely many times. LINKS Alois P. Heinz, Table of n, a(n) for n = 1..10000 MAPLE b:= proc() true end: a:= proc(n) option remember; local h, k, p;       if n=1 then 1     else h:= a(n-1);          for k do p:=parse(cat(h, k));            if b(p) and isprime(p) then break fi          od; b(p):= false; k       fi     end: seq(a(n), n=1..100);  # Alois P. Heinz, Sep 18 2015 PROG (PARI) A077202(nmax)= { local(a, tst, hadp, hSet) ; a=[1] ; hadp=[1] ; for(n=2, nmax, for(new=1, 10000, tst=Str(eval(a[n-1]) eval(new)) ; tst=eval(tst) ; if(isprime(tst), hSet=Set(hadp) ; if( setsearch(hSet, tst)==0, hadp=concat(hadp, tst) ; a=concat(a, new) ; break ; ) ; ) ; ) ; ) ; return(a) ; } { print(A077202(80)) ; } - R. J. Mathar, May 19 2006 CROSSREFS Cf. A082238. Sequence in context: A163117 A099749 A210442 * A086665 A273013 A050521 Adjacent sequences:  A077199 A077200 A077201 * A077203 A077204 A077205 KEYWORD base,nonn AUTHOR Amarnath Murthy, Nov 02 2002 EXTENSIONS Corrected and extended by R. J. Mathar, May 19 2006 Offset corrected by Alois P. Heinz, Sep 18 2015 STATUS approved

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Last modified September 25 07:27 EDT 2021. Contains 347654 sequences. (Running on oeis4.)