A052021 Sum of digits of n is the largest prime factor of n.

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

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