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 A032734 All 81 combinations of prefixing and following a(n) by a single digit are nonprime. 6
 2437, 5620, 7358, 11111, 13308, 13332, 13650, 14612, 19737, 19817, 24217, 25213, 26302, 27971, 28472, 28838, 29289, 29542, 29650, 31328, 33027, 33170, 35914, 35970, 36186, 37977, 38327, 39127, 39608, 40078, 41165, 41528, 42422, 43277 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS Robert Israel, Table of n, a(n) for n = 1..10000 EXAMPLE 2437 prefixed and followed with a pair of digits from (1,2,3,4,5,6,7,8,9) never yields a prime: '9'2437'1' = 7 * 37 * 43 * 83. MAPLE isA032734 := proc(n)         for k from 1 to 9 do         for k2 from 1 to 9 do                 dgs := [k, op(convert(n, base, 10)), k2] ;                 dgsn := add( op(i, dgs)*10^(i-1), i=1..nops(dgs)) ;                 if isprime(dgsn) then                         return false;                 end if;         end do:         end do:         return true; end proc: for n from 1 to 50000 do         if isA032734(n) then                 printf("%d, ", n);         end if; end do: # R. J. Mathar, Oct 22 2011 filter:= proc(n) local d, i, j;      d:= 10^(ilog10(n)+2);      not ormap(isprime, [seq(seq(d*i+10*n+j, j=[1, 3, 5, 7, 9]), i=1..9)]) end proc: select(filter, [\$1..10^5]); # Robert Israel, Jul 07 2016 MATHEMATICA ok[n_] := With[{id = IntegerDigits[n]}, Select[ Flatten[ Table[ FromDigits[ Join[{j}, id, {k}]], {j, 1, 9}, {k, 1, 9}], 1], PrimeQ, 1] == {}]; A032734 = {}; n = 1; While[n < 50000, If[ok[n], Print[n]; AppendTo[A032734, n]]; n++]; A032734(* Jean-François Alcover, Nov 23 2011 *) Select[Range[50000], NoneTrue[Flatten[Table[FromDigits[Join[{x}, IntegerDigits[ #], {y}]], {x, 9}, {y, 9}]], PrimeQ]&] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, Apr 07 2018 *) PROG (PARI) is_A032734(n)=p=10^#Str(n*=10); forstep(k=n+p, n+9*p, p, nextprime(k)>k+9 || return); 1 \\ M. F. Hasler, Oct 22 2011 CROSSREFS Cf. A032682-A032685 and A032702-A032733. Sequence in context: A341286 A250710 A278196 * A345518 A345771 A252047 Adjacent sequences:  A032731 A032732 A032733 * A032735 A032736 A032737 KEYWORD nonn,nice,base AUTHOR Patrick De Geest, May 15 1998 STATUS approved

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Last modified September 27 10:28 EDT 2021. Contains 347689 sequences. (Running on oeis4.)