OFFSET
1,1
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..1000
EXAMPLE
binomial(6+1,6-1)=binomial(7,5)=7!/(5!*2!)=21 --> 2+1=3 prime.
MAPLE
P:=proc(n) local i, k, w; for i from 1 by 1 to n do w:=0; k:=binomial(i+1, i-1); while k>0 do w:=w+k-(trunc(k/10)*10); k:=trunc(k/10); od; if isprime(w) then print(i); fi; od; end: P(1000);
MATHEMATICA
Select[Range[300], PrimeQ[Total[IntegerDigits[Binomial[#+1, #-1]]]]&] (* Harvey P. Dale, Aug 13 2014 *)
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Paolo P. Lava and Giorgio Balzarotti, May 31 2007
STATUS
approved