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%I #26 Jan 24 2022 04:36:02
%S 1,2,3,4,5,6,7,8,9,10,1,12,3,14,15,16,7,18,9,20,21,2,3,24,25,6,27,28,
%T 9,30,3,32,3,14,35,36,7,18,9,40,4,42,4,4,45,6,7,48,49,50,21,12,5,54,5,
%U 56,27,18,9,60,6,6,63,64,15,6,7,28,9,70,7,72,7,14
%N In prime factorization of n: replace each factor with its largest decimal digit.
%H Reinhard Zumkeller, <a href="/A262401/b262401.txt">Table of n, a(n) for n = 1..10000</a>
%F Multiplicative with p -> A054055(p), p prime.
%F a(n) = Product_{k=1..A001222(n)} A054055(A027746(n,k))).
%F a(n) <= n.
%F a(m) = m iff m is 7-smooth:
%F a(A002473(n)) = A002473(n) and a(A068191(n)) < A068191(n).
%F A006530(a(n)) <= 7.
%F a(a(n)) = a(n).
%t Array[Times @@ (Power[Max@ IntegerDigits[#1], #2] & @@@ FactorInteger[#]) &, 74] (* _Michael De Vlieger_, Jan 23 2022 *)
%o (Haskell)
%o a262401 = product . map a054055 . a027746_row'
%o (PARI) a(n) = my(f=factor(n)); for (k=1, #f~, f[k,1] = vecmax(digits(f[k,1]))); factorback(f); \\ _Michel Marcus_, Jan 22 2022
%Y Cf. A054055, A027746, A001222, A002473, A006530, A060418, A068191.
%K nonn,base,mult
%O 1,2
%A _Reinhard Zumkeller_, Sep 25 2015
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