cp's OEIS Frontend

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.

A376740 Numbers that have at least one two-digit prime factor.

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%I A376740 #57 Jun 24 2025 10:37:30
%S A376740 11,13,17,19,22,23,26,29,31,33,34,37,38,39,41,43,44,46,47,51,52,53,55,
%T A376740 57,58,59,61,62,65,66,67,68,69,71,73,74,76,77,78,79,82,83,85,86,87,88,
%U A376740 89,91,92,93,94,95,97,99,102,104,106,110,111,114,115,116,117
%N A376740 Numbers that have at least one two-digit prime factor.
%C A376740 Subsequence of A068191, first differing at A068191(55) = 101 which is not a term here.
%C A376740 Numbers k such that gcd(k,10978895066407230594062391177770267) > 1. - _Chai Wah Wu_, Nov 18 2024 [The big number is A109819(10) - _Alois P. Heinz_, Nov 18 2024]
%C A376740 The asymptotic density of this sequence is A051953(A109819(10))/A109819(10) = 1329644281346285477858013527/2807455661493975149742813527 = 0.473611... . - _Amiram Eldar_, Nov 19 2024
%H A376740 Kishin Ikemoto, <a href="/A376740/b376740.txt">Table of n, a(n) for n = 1..10000</a>
%H A376740 <a href="/index/Rec#order_10978895066407230594062391177770267">Index entries for linear recurrences with constant coefficients</a>, order 10978895066407230594062391177770267.
%F A376740 a(n + A051953(A109819(10))) = a(n) + A109819(10). - _Amiram Eldar_, Nov 19 2024
%e A376740 201 = 3*67 is in this sequence because it has one two-digit prime factor.
%e A376740 202 = 2*101 is not, because neither of them is two-digit.
%p A376740 q:= convert(select(isprime, [seq(i,i=11 .. 99, 2)]),`*`):
%p A376740 filter:= n -> igcd(n,q) > 1:
%p A376740 select(filter, [$1..200]); # _Robert Israel_, Nov 18 2024
%t A376740 A376740Q[k_] := GCD[k, 10978895066407230594062391177770267] > 1;
%t A376740 Select[Range[200], A376740Q] (* _Paolo Xausa_, Jun 24 2025 *)
%o A376740 (Python)
%o A376740 def ok(n): return any(n%p == 0 for p in [11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97])
%o A376740 print([k for k in range(1, 118) if ok(k)]) # _Michael S. Branicky_, Oct 15 2024
%o A376740 (PARI) is(k) = {forprime(p = 11, 97, if(!(k % p), return(1))); 0;} \\ _Amiram Eldar_, Nov 19 2024
%Y A376740 Cf. A051953, A068191, A084891, A109819.
%K A376740 nonn,easy,base
%O A376740 1,1
%A A376740 _Kishin Ikemoto_, Oct 03 2024