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A154586
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Numbers n for which abs((-1)^k*Sum_{k=1..n} ((n-k+1) mod k)) = 0.
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1
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1, 4, 8, 25, 27, 75, 209, 3507, 8466, 16179, 29285, 33987, 175904, 326764, 1161207
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OFFSET
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1,2
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COMMENTS
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LINKS
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FORMULA
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EXAMPLE
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n=8 -> abs(-(8 mod 1) + (7 mod 2) - (6 mod 3) + (5 mod 4) - (4 mod 5) + (3 mod 6) - (2 mod 7) + (1 mod 8)) = abs(-0 + 1 - 0 + 1 - 4 + 3 - 2 + 1) = abs(0) = 0.
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MAPLE
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P:=proc(i) local a, n; for n from 1 to i do a:=abs(add((-1)^k*((n-k+1) mod k), k=1..n)); if a=0 then print(n); fi; od; end: P(100);
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PROG
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(C) #include <stdio.h> int main(int argc, char * argv[]) { for(int n=1;; n++) { unsigned long long a = 0; for(int k=1; k <=n; k += 2) a -= (n-k+1) % k ; for(int k=2; k <=n; k += 2) a += (n-k+1) % k ; if ( a == 0) printf("%d, \n", n) ; } } /* R. J. Mathar, Jan 14 2009 */
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CROSSREFS
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KEYWORD
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more,nonn
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AUTHOR
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EXTENSIONS
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8466 inserted, and sequence extended up to a(13), by R. J. Mathar, Jan 14 2009
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STATUS
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approved
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