|
|
A202707
|
|
Numbers n such that (sum of digits of n!!) / 9 is prime.
|
|
0
|
|
|
9, 11, 12, 13, 14, 15, 16, 18, 19, 21, 22, 25, 26, 28, 48, 51, 57, 60, 70, 72, 74, 78, 80, 81, 82, 86, 89, 92, 103, 109, 111, 114, 120, 125, 128, 130, 131, 142, 145, 146, 151, 155, 157, 159, 164, 168, 169, 179, 183, 185, 186, 191, 195, 197, 200, 205, 210, 211
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
COMMENTS
|
If n = 9 and n >10, then (sum of digits of n!!) / 9 is an integer (see A120390).
|
|
LINKS
|
|
|
FORMULA
|
|
|
EXAMPLE
|
For n = 9, 9!! = 945, and (9+4+5)/9 = 2 is prime.
|
|
MATHEMATICA
|
lst={}; Do[If[PrimeQ[Sum[DigitCount[n!!][[i]]*i/9, {i, 1, 9}]], AppendTo[lst, n]], {n, 1, 300}]; lst
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn,base
|
|
AUTHOR
|
|
|
STATUS
|
approved
|
|
|
|