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Numbers with a sum of digits equal to their smallest prime factor.
1

%I #8 Apr 17 2019 03:44:20

%S 2,3,5,7,20,21,110,111,133,200,201,209,247,407,481,511,629,803,1010,

%T 1011,1100,1101,1141,1387,1417,1651,1679,1853,2000,2001,2023,2119,

%U 2159,2353,2401,2771,3031,3077,3097,3383,3439,3523,3749,3781,4577,4607,4913,5149,5161

%N Numbers with a sum of digits equal to their smallest prime factor.

%H Robert Israel, <a href="/A162948/b162948.txt">Table of n, a(n) for n = 1..10000</a>

%F {n: A007953(n) = A020639(n)}. - _R. J. Mathar_, Jul 19 2009

%e 133 is in the sequence because 1 + 3 + 3 = 7 and 7 is the smallest prime factor of 133.

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

%p A020639 := proc(n) min(op(numtheory[factorset](n) )) ; end:

%p isA162948 := proc(n) RETURN( A007953(n) = A020639(n)) ; end:

%p for n from 1 to 6000 do if isA162948(n) then printf("%d,",n) ; fi; od: # _R. J. Mathar_, Jul 19 2009

%Y Cf: A007953, A020639.

%Y Even terms: A069537.

%K nonn,base

%O 1,1

%A _Claudio Meller_, Jul 18 2009

%E Single-digit primes added by _R. J. Mathar_, Jul 19 2009