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A032734
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All 81 combinations of prefixing and following a(n) by a single digit are nonprime.
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4
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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; internal format)
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OFFSET
| 1,1
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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 x 37 x 43 x 83.
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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
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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(* From Jean-François Alcover, Nov 23 2011 *)
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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
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CROSSREFS
| Cf. A032682-A032685 and A032702-A032733.
Sequence in context: A202201 A147984 A192767 * A083625 A183629 A035772
Adjacent sequences: A032731 A032732 A032733 * A032735 A032736 A032737
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KEYWORD
| nonn,nice,base
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AUTHOR
| Patrick De Geest (pdg(AT)worldofnumbers.com), May 15 1998.
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