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 A125268 Numbers that end with decimal digit 1, 3, 7, or 9 and that produce only composite numbers when any of the digits 0,1,...,9 is inserted anywhere in them (including at the beginning or end). 2
 25011, 52647, 72753, 122313, 168699, 283251, 324021, 598041, 783441, 804131, 837207, 924807, 1247241, 1905759, 2514819, 3461101, 3514077, 3617389, 3905817, 4112913, 4142139, 4203151, 4229871, 4283679, 4531907, 4628827, 4828443, 5380413, 5478091, 5632671, 5714889, 5818569, 5989269, 5990961 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS Since digit 0 can be inserted at the beginning of a term, each term must be composite. LINKS Max Alekseyev, Table of n, a(n) for n = 1..972 (all terms below 10^8) MAPLE filter:= proc(n) local x, y, d, t; x:= n; y:= 0; for d from 0 to ilog10(n)+1 do for t from 0 to 9 do if isprime(10^(d+1)*x+10^d*t + y) then return false fi; od; t:= x mod 10; y:= y + 10^d*t; x:= (x-t)/10; od; true end proc: select(filter, [seq(seq(10*i+j, j=[1, 3, 7, 9]), i=0..10^6)]); # Robert Israel, Sep 12 2016 PROG (PARI) { printA125268(U=8) = my(v, t); v=vector(10^U); forprime(p=11, 10^(U+1), if(p<=U, v[p]=p); for(i=1, #Str(p), t=(p\10^i) * 10^(i-1) + (p%10^(i-1)); if(#Str(t)==#Str(p)-1, v[t]=p); ); ); forstep(n=1, 10^U, 2, if(n%10==5||v[n], next); print1(n, ", "); ); } \\ prints terms below 10^U, by Max Alekseyev, Sep 12 2016 CROSSREFS Cf. A003459, A124665 Sequence in context: A252846 A031651 A263815 * A212726 A258542 A205041 Adjacent sequences: A125265 A125266 A125267 * A125269 A125270 A125271 KEYWORD nonn,base AUTHOR I. J. Kennedy, Jan 15 2007 EXTENSIONS Corrected and extended by Robert G. Wilson v, Jan 26 2007 Removed incorrect terms and extended by Max Alekseyev, Sep 12 2016 STATUS approved

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Last modified September 21 21:57 EDT 2023. Contains 365503 sequences. (Running on oeis4.)