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 A176554 #7 Jul 09 2021 16:12:45 %S A176554 1,2,4,5,6,8,10,11,12,14,15,16,17,18,19,20,22,23,24,25,26,27,28,29,30, %T A176554 32,33,34,35,36,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55, %U A176554 56,57,58,59,60,61,62,63,64,65,66,68,69,70,71,72,74,75,76,77,78,80,81 %N A176554 Numbers n such that concatenations of divisors of n are nonprime. %C A176554 See A037278(n) = concatenation of divisors of n. See A176556 for corresponding values of concatenations. Complement of A176553(n) for n >= 2. %H A176554 Harvey P. Dale, <a href="/A176554/b176554.txt">Table of n, a(n) for n = 1..1000</a> %e A176554 a(6) = 8: divisors of 8 are 1,2,4,8 and their concatenation 1248 is nonprime. %t A176554 Select[Range[100],!PrimeQ[FromDigits[Flatten[IntegerDigits/@ Divisors[ #]]]]&] (* _Harvey P. Dale_, Jul 09 2021 *) %K A176554 nonn,base %O A176554 1,2 %A A176554 _Jaroslav Krizek_, Apr 20 2010 %E A176554 Edited and extended by _Charles R Greathouse IV_, Apr 30 2010