OFFSET
1,2
COMMENTS
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.
FORMULA
a(n) = (A347253(n) - 6)/10.
Lim_{n->infinity} a(n)/a(n-1) = 1.
EXAMPLE
13 is a term because 4*34 = 136 = 13*10 + 6.
MATHEMATICA
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
PROG
(Python)
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))
print(aupto(197)) # Michael S. Branicky, Aug 24 2021
(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
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Stefano Spezia, Aug 24 2021
STATUS
approved