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%I #19 Aug 21 2024 12:26:39
%S 1,3,7,13,27,31,49,57,63,81,91,97,99,103,109,117,123,129,151,153,181,
%T 187,193,201,213,231,237,259,279,297,301,319,327,367,409,423,427,439,
%U 459,483,487,493,523,543,553,559,571,579,601,609,613,621,627,657,669
%N Numbers which yield primes when a 1 is prefixed or appended.
%e 57 is a term as 157 as well as 571 are primes.
%p i := 0:for k from 1 to 3200 do if(isprime(1+10*k) and isprime(k+10^(ceil(evalf(log(k+1)/log(10))))*1)) then s[i] := k; i := i+1; end if; end do:q := seq(s[j],j=0..i-1);
%t p1Q[n_]:=Module[{idn=IntegerDigits[n]},PrimeQ[FromDigits[Join[{1}, idn]]] && PrimeQ[FromDigits[Join[idn,{1}]]]]; Select[Range[700],p1Q] (* _Harvey P. Dale_, Jan 23 2013 *)
%t Flatten@Position[{#+10^IntegerLength@#,1+10*#}&/@Range@10000,{_?PrimeQ..}] (* _Hans Rudolf Widmer_, Aug 21 2024 *)
%K base,easy,nonn
%O 1,2
%A _Amarnath Murthy_, Mar 02 2002
%E More terms from _Sascha Kurz_, Mar 17 2002