This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A374331 #26 Jul 10 2024 14:03:55 %S A374331 6,717,989,13231,15251,15751,18281,19291,31613,34043,35653,37073, %T A374331 37673,38383,38683,97079,98789,99899,1115111,1226221,1794971,3525253, %U A374331 3755573,3782873,104646401,114202411,127888721,133707331,134010431,137181731,138050831,146828641,157494751,157585751,161555161 %N A374331 Palindromic squarefree semiprimes such that the sum of the two prime factors is also a palindrome. %e A374331 717 is a term because 717 = 3*239 and 3 + 239 = 242. %t A374331 Select[Range[10^6], PalindromeQ[#] && SquareFreeQ[#] && PrimeNu[#]==2 && PalindromeQ[Total[First/@FactorInteger[#]]]&] (* _Stefano Spezia_, Jul 06 2024 *) %o A374331 (PARI) ispal(n)=my(d=digits(n));d==Vecrev(d) \\ %o A374331 for(a=2,10^10,if(omega(a)==2&&bigomega(a)==2 &&ispal(a),b=factor(a)[1,1]+factor(a)[2,1]; if(ispal(b),print1(a,",")))) %o A374331 (PARI) isok(k) = if (issquarefree(k) && ispal(k), my(f=factor(k)); (bigomega(f)==2) && ispal(f[1,1]+f[2,1])); \\ _Michel Marcus_, Jul 05 2024 %Y A374331 Cf. A002113, A006881. %K A374331 nonn,base %O A374331 1,1 %A A374331 _Alexandru Petrescu_, Jul 05 2024