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A052021 Sum of digits of n is the largest prime factor of n. 7
2, 3, 5, 7, 12, 50, 70, 308, 320, 364, 476, 500, 605, 700, 704, 715, 832, 935, 1088, 1183, 1547, 1729, 2401, 2584, 2618, 2704, 2926, 3080, 3200, 3536, 3640, 3952, 4225, 4760, 4784, 4913, 5000, 5491, 5525, 5819, 5831, 6050, 6175, 6517, 6647, 7000, 7040, 7150 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

FORMULA

{n: A007953(n) = A006530(n)}. - R. J. Mathar, May 30 2010

EXAMPLE

13685 has sum of digits '23' and 13685 = 5*7*17*'23'.

MAPLE

A007953 := proc(n) add(d, d=convert(n, base, 10)) ; end proc:

A006530 := proc(n) numtheory[factorset](n) ; max(op(%)) ; end proc:

for n from 1 to 8000 do if A007953(n) = A006530(n) then printf("%d, ", n) ; end if; end do: # R. J. Mathar, May 30 2010

MATHEMATICA

Select[Range[2, 8000], FactorInteger[#][[-1, 1]]==Total[IntegerDigits[#]]&] (* Harvey P. Dale, Oct 17 2012 *)

PROG

(Haskell)

a052021 n = a052021_list !! (n-1)

a052021_list = tail $ filter (\x -> a007953 x == a006530 x) [1..]

-- Reinhard Zumkeller, Nov 06 2011

CROSSREFS

Cf. A052018, A052019, A052020, A052022, A007953, A005349, A028834.

Sequence in context: A273728 A117593 A209192 * A217396 A126057 A126056

Adjacent sequences:  A052018 A052019 A052020 * A052022 A052023 A052024

KEYWORD

nonn,base,nice

AUTHOR

Patrick De Geest, Nov 15 1999

EXTENSIONS

Single-digit primes added by R. J. Mathar, May 30 2010

Offset corrected by Reinhard Zumkeller, Nov 05 2011

STATUS

approved

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Last modified August 18 10:51 EDT 2017. Contains 290710 sequences.