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 A263865 #16 May 23 2025 10:14:31 %S A263865 1,337,2293,4327,6247,6269,12749,13603,14023,14347,14407,15997,21673, %T A263865 25229,31511,36971,47107,48703,48959,50171,56351,59399,63389,69427, %U A263865 83381,84491,85061,104549,107857,109649,118567 %N A263865 Odd k for which abs(2^m - k) is nonprime for all m < k. %C A263865 Related to the problem in A076337. %o A263865 (PARI) forstep(k=1, 6269, 2, c=m=0; while(m<k, if(ispseudoprime(abs(2^m-k)), c=1; break); m++); if(c==0, print1(k, ", "))); %o A263865 (Python) %o A263865 from gmpy2 import is_prime %o A263865 def ok(k): return k&1 and all(not is_prime(abs((1<<m)-k)) for m in range(k)) %o A263865 print([k for k in range(1, 7000, 2) if ok(k)]) # _Michael S. Branicky_, May 22 2025 %Y A263865 Cf. A076337, A101036. %K A263865 nonn,more %O A263865 1,2 %A A263865 _Arkadiusz Wesolowski_, Oct 28 2015 %E A263865 a(20)-a(31) from _Michael S. Branicky_, May 22 2025