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 A217047 Primes that remain prime when a single "8" digit is inserted between any two adjacent digits. 8
 11, 23, 47, 83, 131, 173, 179, 233, 353, 389, 521, 569, 641, 683, 839, 887, 911, 971, 983, 1229, 1289, 1913, 2087, 2663, 2837, 2879, 3329, 3671, 3677, 3803, 3821, 4259, 4409, 4817, 4871, 4889, 5237, 5477, 5693, 6449, 6581, 6863, 7283, 7487, 7583, 7823, 7853 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Paolo P. Lava, Table of n, a(n) for n = 1..200 EXAMPLE 325421 is prime and also 3254281, 3254821, 3258421, 3285421 and 3825421. MAPLE with(numtheory); A217044:=proc(q, x) local a, b, c, i, n, ok; for n from 5 to q do a:=ithprime(n); b:=0; while a>0 do b:=b+1; a:=trunc(a/10); od; a:=ithprime(n); ok:=1;   for i from 1 to b-1 do     c:=a+9*10^i*trunc(a/10^i)+10^i*x;     if not isprime(c) then ok:=0; break; fi; od;   if ok=1 then print(ithprime(n)); fi; od; end: A217044(100000, 8) PROG (PARI) is(n)=my(v=concat([""], digits(n))); for(i=2, #v-1, v[1]=Str(v[1], v[i]); v[i]=8; if(i>2, v[i-1]=""); if(!isprime(eval(concat(v))), return(0))); isprime(n) \\ Charles R Greathouse IV, Sep 25 2012 (MAGMA) [p: p in PrimesInInterval(11, 8000) | forall{m: t in [1..#Intseq(p)-1] | IsPrime(m) where m is (Floor(p/10^t)*10+8)*10^t+p mod 10^t}]; // Bruno Berselli, Sep 26 2012 CROSSREFS Cf. A050674, A050711-A050719, A069246, A159236, A215417, A215419-A215421, A217044-A217046. Sequence in context: A161897 A282531 A145994 * A139834 A100558 A126199 Adjacent sequences:  A217044 A217045 A217046 * A217048 A217049 A217050 KEYWORD nonn,base AUTHOR Paolo P. Lava, Sep 25 2012 STATUS approved

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Last modified October 14 07:31 EDT 2019. Contains 327995 sequences. (Running on oeis4.)