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%I #18 Nov 13 2021 22:39:36
%S 12,16,22,30,34,36,45,48,55,58,61,72,78,84,85,87,90,96,100,108,111,
%T 112,114,121,124,126,133,135,141,142,144,150,154,156,159,165,166,168,
%U 175,177,178,184,189,192,196,198,199,202,204,205,210,219,220,226,232,240
%N Nontrivial numbers in which inserting, prefixing or suffixing a 1 anywhere yields only composite numbers.
%C This excludes numbers == 2 mod 3 (A016789).
%e 26 is a member as the three numbers 126, 216 and 261 obtained by placing a 1 at all possible places are composite.
%p anz := 0:for i from 1 to 1500 do b := convert(i,base,10):s := sum(b[l],l=1..nops(b)): if((s mod 3)<>2) then 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:fi:od:seq(a[l],l=1..anz); # _Sascha Kurz_, Jan 26 2003
%Y Cf. A002808, A016789, A070328.
%K base,nonn
%O 1,1
%A _Amarnath Murthy_, May 11 2002
%E More terms from _Olaf Voß_, Jan 21 2003
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