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 A345217 a(n) is the first emirp that starts a chain of exactly n emirps under the mapping f(x) = x + reverse(x) + 1. 0
 13, 149, 70949, 12314597 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(n) == 5 (mod 6) for n >= 2. No more terms < 16*10^11. - Lars Blomberg, Jun 25 2021 LINKS Table of n, a(n) for n=1..4. EXAMPLE a(1) = 13 is the first emirp, but 13+31+1 = 45 is not an emirp. a(2) = 149 because 149 and 149+941+1 = 1091 are emirps, but 1091+1901+1 = 2993 is not an emirp. a(3) = 70949 because 70949, 70949+94907+1 = 165857, and 165857+758561 = 924419 are emirps, but 924419+914429+1 = 1838849 is not an emirp. MAPLE revdigs:= proc(n) local L, i; L:= convert(n, base, 10); add(L[-i]*10^(i-1), i=1..nops(L)) end proc: f:= proc(n) local r, t, x; x:= n; for t from 0 do if not isprime(x) then return t fi; r:= revdigs(x); if not (r <> n and isprime(x) and isprime(r)) then return t fi; x:= x+r+1; od; end proc: V:= Vector(4): V[1]:= 13: count:= 1: for n from 17 by 6 while count < 4 do v:= f(n); if v > 0 and V[v] = 0 then V[v]:= n; count:= count+1 fi; od: convert(V, list); CROSSREFS Cf. A006567. Sequence in context: A125448 A163148 A355414 * A185405 A051475 A242576 Adjacent sequences: A345214 A345215 A345216 * A345218 A345219 A345220 KEYWORD nonn,base,more AUTHOR J. M. Bergot and Robert Israel, Jun 10 2021 STATUS approved

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Last modified December 11 11:45 EST 2023. Contains 367725 sequences. (Running on oeis4.)