

A332261


Numbers that yield a prime whenever a '4' is inserted between any two digits.


0



0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 19, 21, 37, 39, 43, 49, 51, 57, 61, 63, 67, 73, 91, 97, 109, 129, 147, 153, 159, 171, 187, 199, 211, 223, 237, 241, 247, 259, 267, 333, 349, 357, 363, 409, 421, 423, 441, 447, 457, 463, 493, 517, 537, 541, 543, 549, 571, 579, 583, 627, 649, 681
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OFFSET

1,3


COMMENTS

For singledigit terms, the condition is voidly satisfied: nothing can be inserted.


LINKS



EXAMPLE

10281 is in this sequence because 1(4)0281, 10(4)281, 102(4)81, and 1028(4)1 are all prime.


PROG

(Magma) a:=[]; for k in [1..700] do s:=0; v:=Reverse(Intseq(k)); for i in [1..#v1] do vv:=v[1..i] cat [4] cat v[i+1..#v]; p:=Seqint(Reverse(vv)); if not IsPrime(p) then break; else s:=s+1; end if; end for; if s eq #v1 then Append(~a, k); end if; end for; [0] cat a; // Marius A. Burtea, Feb 09 2020


CROSSREFS



KEYWORD

nonn,base


AUTHOR



STATUS

approved



