A307046 - OEIS

%I #44 Apr 02 2019 11:57:20

%S 4,28,40,62,106,140,193,196,274,316,334,400,410,554,556,620,862,866,

%T 874,884,962,1004,1025,1066,1154,1174,1190,1205,1256,1274,1294,1360,

%U 1390,1394,1396,1400,1744,1784,1816,1844,1891,1900,1927,1960,1981,1988,2672,2696,2710,2722,2740,2786,2800,3016,3026

%N Numbers k such that k^2 reversed is a prime and k^2 + (k^2 reversed) is a semiprime.

%H Robert Israel, <a href="/A307046/b307046.txt">Table of n, a(n) for n = 1..10000</a>

%e 4^2=16, reversed is 61. 16+61=77 which is semiprime (7*11), so 4 is in this sequence.

%p revdigs:= proc(n) local L,i;

%p L:= convert(n,base,10);

%p add(L[-i]*10^(i-1),i=1..nops(L))

%p end proc:

%p filter:= proc(n) local a,b;

%p a:= n^2;

%p b:= revdigs(a);

%p isprime(b) and numtheory:-bigomega(a+b)=2

%p end proc:

%p select(filter, [$1..10000]); # _Robert Israel_, Mar 31 2019

%t Select[Range[50000],

%t PrimeQ[IntegerReverse[#^2]] &&

%t    PrimeOmega[#^2 + IntegerReverse[#^2]] == 2 &]

%Y Cf. A007488, A059007, A306301.

%K nonn,base

%O 1,1

%A _Robert Price_, Mar 31 2019