cp's OEIS Frontend

A347254 Positive integers k such that 10*k+6 is equal to the product of two integers ending with 4 (A347253).

%I A347254 #12 Oct 04 2021 09:02:28
%S A347254 1,5,9,13,17,19,21,25,29,33,37,41,45,47,49,53,57,61,65,69,73,75,77,81,
%T A347254 85,89,93,97,101,103,105,109,113,115,117,121,125,129,131,133,137,141,
%U A347254 145,149,153,157,159,161,165,169,173,177,181,183,185,187,189,193,197
%N A347254 Positive integers k such that 10*k+6 is equal to the product of two integers ending with 4 (A347253).
%C A347254 Since an integer 10*k + 6 = (10*a + 4)*(10*b + 4) implies that k = 10*a*b + 4*(a + b) + 1, all the terms of this sequence are odd.
%F A347254 a(n) = (A347253(n) - 6)/10.
%F A347254 Lim_{n->infinity} a(n)/a(n-1) = 1.
%e A347254 13 is a term because 4*34 = 136 = 13*10 + 6.
%t A347254 a={}; For[n=0, n<=200, n++, For[k=0, k<=n, k++, If[Mod[10*n+6, 10*k+4]==0 && Mod[(10*n+6)/(10*k+4), 10]==4 && n>Max[a], AppendTo[a, n]]]]; a
%o A347254 (Python)
%o A347254 def aupto(lim): return sorted(set(a*b//10 for a in range(4, 10*lim//4+3, 10) for b in range(a, 10*lim//a+3, 10) if a*b//10 <= lim))
%o A347254 print(aupto(197)) # _Michael S. Branicky_, Aug 24 2021
%o A347254 (PARI) isok(k) =  my(x=10*k+6); sumdiv(x, d, (Mod(d, 10)==4) && Mod(x/d, 10)==4); \\ _Michel Marcus_, Oct 04 2021
%Y A347254 Cf. A016873 (ending with 5), A017341, A324298 (ending with 6), A346951 (ending with 3), A347253.
%K A347254 nonn,base
%O A347254 1,2
%A A347254 _Stefano Spezia_, Aug 24 2021