The OEIS is supported by the many generous donors to the OEIS Foundation.

 Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 60th year, we have over 367,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”). Other ways to Give
 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS For single-digit terms, the condition is voidly satisfied: nothing can be inserted. LINKS Table of n, a(n) for n=1..62. 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..#v-1] 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 #v-1 then Append(~a, k); end if; end for; [0] cat a; // Marius A. Burtea, Feb 09 2020 CROSSREFS Cf. A164329, A304246, A304247, A304248, A050714. Sequence in context: A087121 A087052 A077557 * A075517 A248013 A088473 Adjacent sequences: A332258 A332259 A332260 * A332262 A332263 A332264 KEYWORD nonn,base AUTHOR Eric Fox, Feb 08 2020 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recents
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 7 18:28 EST 2023. Contains 367660 sequences. (Running on oeis4.)