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A262401
In prime factorization of n: replace each factor with its largest decimal digit.
4
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, 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, 56, 27, 18, 9, 60, 6, 6, 63, 64, 15, 6, 7, 28, 9, 70, 7, 72, 7, 14
OFFSET
1,2
LINKS
FORMULA
Multiplicative with p -> A054055(p), p prime.
a(n) = Product_{k=1..A001222(n)} A054055(A027746(n,k))).
a(n) <= n.
a(m) = m iff m is 7-smooth:
a(A002473(n)) = A002473(n) and a(A068191(n)) < A068191(n).
A006530(a(n)) <= 7.
a(a(n)) = a(n).
MATHEMATICA
Array[Times @@ (Power[Max@ IntegerDigits[#1], #2] & @@@ FactorInteger[#]) &, 74] (* Michael De Vlieger, Jan 23 2022 *)
PROG
(Haskell)
a262401 = product . map a054055 . a027746_row'
(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
KEYWORD
nonn,base,mult
AUTHOR
Reinhard Zumkeller, Sep 25 2015
STATUS
approved