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A068673
Numbers which yield primes when a 1 is prefixed or appended.
18
1, 3, 7, 13, 27, 31, 49, 57, 63, 81, 91, 97, 99, 103, 109, 117, 123, 129, 151, 153, 181, 187, 193, 201, 213, 231, 237, 259, 279, 297, 301, 319, 327, 367, 409, 423, 427, 439, 459, 483, 487, 493, 523, 543, 553, 559, 571, 579, 601, 609, 613, 621, 627, 657, 669
OFFSET
1,2
EXAMPLE
57 is a term as 157 as well as 571 are primes.
MAPLE
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);
MATHEMATICA
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 *)
Flatten@Position[{#+10^IntegerLength@#, 1+10*#}&/@Range@10000, {_?PrimeQ..}] (* Hans Rudolf Widmer, Aug 21 2024 *)
CROSSREFS
Sequence in context: A205521 A125898 A146928 * A298360 A140465 A333653
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Mar 02 2002
EXTENSIONS
More terms from Sascha Kurz, Mar 17 2002
STATUS
approved