OFFSET
1,1
COMMENTS
Conjecture: except for the initial term, each term is one less than a multiple of 9. - Harvey P. Dale, Dec 02 2016
LINKS
Harvey P. Dale, Table of n, a(n) for n = 1..5000
FORMULA
EXAMPLE
The product of the first twin primes is 15=3*5, and sum of digits of 15 is 6.
MATHEMATICA
a = {6}; Do[If[PrimeQ[6n - 1] && PrimeQ[6n + 1], c = IntegerDigits[36n^2 - 1]; b = Total[c]; AppendTo[a, b]], {n, 400}]; a
Total[IntegerDigits[Times@@#]]&/@Select[Partition[Prime[Range[500]], 2, 1], #[[2]]- #[[1]]==2&] (* Harvey P. Dale, Dec 02 2016 *)
PROG
(PARI) lista(nn) = for (x=1, nn, if(prime(x+1)-prime(x)==2, print1(sumdigits(prime(x)*prime(x+1)), ", "))); \\ Michel Marcus, Nov 04 2013
CROSSREFS
KEYWORD
nonn,base
AUTHOR
Artur Jasinski, Dec 12 2007
EXTENSIONS
First term a(1)=6 inserted by Michel Marcus, Nov 04 2013
STATUS
approved