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A154701
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Numbers k such that k, k + 1 and k + 2 are 3 consecutive Harshad numbers.
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33
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1, 2, 3, 4, 5, 6, 7, 8, 110, 510, 511, 1010, 1014, 1015, 2022, 2023, 2464, 3030, 3031, 4912, 5054, 5831, 7360, 8203, 9854, 10010, 10094, 10307, 10308, 11645, 12102, 12103, 12255, 12256, 13110, 13111, 13116, 13880, 14704, 15134, 17152, 17575, 18238, 19600, 19682
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OFFSET
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1,2
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COMMENTS
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Harshad numbers are also known as Niven numbers.
Cooper and Kennedy proved that there are infinitely many runs of 20 consecutive Niven numbers. Therefore this sequence is infinite. - Amiram Eldar, Jan 03 2020
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REFERENCES
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Jean-Marie De Koninck, Those Fascinating Numbers, American Mathematical Society, 2009, p. 36, entry 110.
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LINKS
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EXAMPLE
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110 is a term since 110 is divisible by 1 + 1 + 0 = 2, 111 is divisible by 1 + 1 + 1 = 3, and 112 is divisible by 1 + 1 + 2 = 4.
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MAPLE
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Res:= NULL: count:= 0:
state:= 1:
L:= [1]:
for n from 2 while count < 100 do
L[1]:=L[1]+1;
for k from 1 while L[k]=10 do L[k]:= 0;
if k = nops(L) then L:= [0$nops(L), 1]; break
else L[k+1]:= L[k+1]+1 fi
od:
s:= convert(L, `+`);
if n mod s = 0 then
state:= min(state+1, 3);
if state = 3 then count:= count+1; Res:= Res, n-2; fi
else state:= 0
fi
od:
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MATHEMATICA
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nivenQ[n_] := Divisible[n, Total @ IntegerDigits[n]]; niv = nivenQ /@ Range[3]; seq = {}; Do[niv = Join[Rest[niv], {nivenQ[k]}]; If[And @@ niv, AppendTo[seq, k - 2]], {k, 3, 2*10^4}]; seq (* Amiram Eldar, Jan 03 2020 *)
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PROG
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(C) #include <stdio.h>
#include <conio.h>
int is_harshad(int n){
int i, j, count=0;
i=n;
while(i>0){
count=count+i%10;
i=i/10;
}
return n%count==0?1:0;
}
main(){
int k;
clrscr();
for(k=1; k<=30000; k++)
if(is_harshad(k)&&is_harshad(k+1)&&is_harshad(k+2))
printf("%d, ", k);
getch();
return 0;
}
(Magma) f:=func<n|n mod &+Intseq(n) eq 0>; a:=[]; for k in [1..20000] do if forall{m:m in [0..2]|f(k+m)} then Append(~a, k); end if; end for; a; // Marius A. Burtea, Jan 03 2020
(Python)
from itertools import count, islice
def agen(): # generator of terms
h1, h2, h3 = 1, 2, 3
while True:
if h3 - h1 == 2: yield h1
h1, h2, h3 = h2, h3, next(k for k in count(h3+1) if k%sum(map(int, str(k))) == 0)
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CROSSREFS
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KEYWORD
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nonn,base
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AUTHOR
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Avik Roy (avik_3.1416(AT)yahoo.co.in), Jan 14 2009, Jan 15 2009
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STATUS
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approved
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