A397431 - OEIS

%I #14 Jul 07 2026 21:35:11

%S 55,77,91,143,203,275,295,323,355,395,407,415,515,517,533,535,553,559,

%T 575,595,637,671,703,731,755,767,847,895,943,1037,1043,1067,1079,1081,

%U 1111,1147,1157,1159,1183,1189,1243,1267,1271,1331,1333,1357,1363,1391,1411,1435,1463,1507

%N Composites in A161601 whose binary reversal is prime.

%H Vincenzo Librandi, <a href="/A397431/b397431.txt">Table of n, a(n) for n = 1..34316</a>

%t p[f_] := Module[{n = 1, c = 0}, Reap[While[c < f, With[{d = IntegerDigits[n, 2]}, With[{r = Reverse[d]}, If[d =!= r && n < FromDigits[r, 2],

%t Sow[{n, FromDigits[r, 2]}]; c++]]]; n += 2]][[2, 1]]];

%t u = Select[p[300], !PrimeQ[#[[1]]] && PrimeQ[#[[2]]] &];

%t Map[First, u]

%t (* _Peter J. C. Moses_, Jun 24 2026 *)

%Y Cf. A000040, A002808, A161601, A161603, A397429, A397430, A397432.

%K nonn,easy,base,new

%O 1,1

%A _Clark Kimberling_, Jun 24 2026

%E a(40) corrected and more terms from _Vincenzo Librandi_, Jul 07 2026