Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%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