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 A070328 Numbers in which inserting, prefixing or suffixing a 1 anywhere yields only composite numbers. 1
 2, 5, 8, 11, 12, 14, 16, 17, 20, 22, 23, 26, 29, 30, 32, 34, 35, 36, 38, 41, 44, 45, 47, 48, 50, 53, 55, 56, 58, 59, 61, 62, 65, 68, 71, 72, 74, 77, 78, 80, 83, 84, 85, 86, 87, 89, 90, 92, 95, 96, 98, 100, 101, 104, 107, 108, 110, 111, 112, 113, 114, 116, 119, 121, 122 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,1 LINKS EXAMPLE 26 is a member as the three numbers 126, 216 and 261 obtained by placing a 1 at all possible places are composite. MAPLE anz := 0:for i from 2 to 1500 do b := convert(i, base, 10):s := sum(b[l], l=1..nops(b)): ok := true:for j from 0 to nops(b) do q := sum(b[k]*10^(k-1), k=1..j):q := q+10^(j): q := q+sum(b[k]*10^k, k=j+1..nops(b)): if(isprime(q)) then ok := false:fi:od: if(ok=true) then anz := anz+1:a[anz] := i:fi:od:seq(a[l], l=1..anz); CROSSREFS Cf. A070329. Sequence in context: A143263 A327138 A102624 * A124934 A125217 A277574 Adjacent sequences:  A070325 A070326 A070327 * A070329 A070330 A070331 KEYWORD base,nonn AUTHOR Amarnath Murthy, May 11 2002 EXTENSIONS Corrected and extended by Sascha Kurz, Jan 26 2003 STATUS approved

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Last modified August 5 18:00 EDT 2021. Contains 346488 sequences. (Running on oeis4.)