OFFSET
1,3
COMMENTS
The sum of the first 23 primes gives 874 = 23*38, see A045345. - Alois P. Heinz, Aug 02 2009
LINKS
Alois P. Heinz, Table of n, a(n) for n = 1..100
EXAMPLE
a(4) = 5: prime(4) = 7 and the five sets are (5+7)/2 = 6, 7/1 = 7, (3+7)/2 = 5, (2+3+7)/3 = 4, (3+5+7)/3 = 5.
MAPLE
b:= proc(t, i, m, h) option remember; if h=0 then `if` (t=0, 1, 0) elif i<1 or h>i then 0 else b (t, i-1, m, h) +b((t+ithprime(i)) mod m, i-1, m, h-1) fi end: a:= n-> add(b(ithprime(n) mod m, n-1, m, m-1), m=1..n): seq (a(n), n=1..40); # Alois P. Heinz, Aug 02 2009
MATHEMATICA
f[n_] := Block[{c = 0, k = n, lst = Prime@ Range@n, np = Prime@n, slst}, While[k < 2^n, slst = Subsets[lst, All, {k}]; If[Last@slst == np && Mod[Plus @@ slst, Length@slst] == 0, c++ ]; k++ ]; c]; Do[ Print[{n, f@n} // Timing], {n, 24}] (* Robert G. Wilson v *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Naohiro Nomoto, May 03 2003
EXTENSIONS
a(22)-a(24) from Robert G. Wilson v, Jan 19 2007
Corrected a(23) and extended by Alois P. Heinz, Aug 02 2009
STATUS
approved