cp's OEIS Frontend

A088281 a(1) = 11; for n > 1, palindromic primes in which a single digit is sandwiched between strings of '1's.

%I A088281 #15 Nov 04 2024 14:25:42
%S A088281 11,101,131,151,181,191,11311,11411,1114111,1117111,111181111,
%T A088281 111191111,1111118111111,111111151111111,111111181111111,
%U A088281 111111111161111111111,11111111111111611111111111111,111111111111111111131111111111111111111,11111111111111111111111111911111111111111111111111111
%N A088281 a(1) = 11; for n > 1, palindromic primes in which a single digit is sandwiched between strings of '1's.
%C A088281 For n > 1, near-repunit palindromic primes (or, palindromic terms of A105992). - _Lekraj Beedassy_, Jun 05 2009
%H A088281 Harvey P. Dale, <a href="/A088281/b088281.txt">Table of n, a(n) for n = 0..32</a>
%H A088281 <a href="/index/Pri#primes_involving_repunits_.2C_sequences_related_to_:">Index to OEIS entries related to primes involving repdigits</a>.
%t A088281 Join[{11},Select[Flatten[Table[FromDigits[Join[PadRight[{},n,1],{d},PadRight[{},n,1]]],{n,26},{d,Cases[Range[0,9],Except[1]]}]],PrimeQ]] (* _Harvey P. Dale_, Nov 04 2024 *)
%o A088281 (PARI) print1(11); for(L=1,19,for(d=0,9,d!=1 && ispseudoprime(p=10^(2*L+1)\9+(d-1)*10^L) && print1(","p))) \\ _M. F. Hasler_, Feb 07 2020
%Y A088281 Cf. A088282, A088283, A088284 (analog with string of '3's, '7's resp. '9's).
%Y A088281 Cf. A105992 (near-repunit primes), A065074 (which contain the digit 0), A034093 (number of primes by changing one 1 to 0), A065083 (least k for which that = n).
%Y A088281 Cf. A164937 (near-repdigit primes); with 2, ..., 9 as repeated digit: A105982, A105981, A105980, A105979, A105978, A105977, A105976, A105975.
%K A088281 base,nonn
%O A088281 0,1
%A A088281 _Amarnath Murthy_, Sep 29 2003
%E A088281 More terms from _David Wasserman_, Aug 03 2005
%E A088281 Offset changed from 0 to 1 by _Lekraj Beedassy_, Jun 05 2009
%E A088281 Edited by _M. F. Hasler_, Feb 07 2020