OFFSET
0,3
LINKS
Rémy Sigrist, Table of n, a(n) for n = 0..10000
EXAMPLE
a(12) = 1*2 = 2, a(12345) = 1*5 + 2*4 + 3*3 = 22.
MATHEMATICA
Array[Sum[#1[[k]]*#1[[#2 + 1 - k]], {k, Ceiling[#2/2]}] & @@ {IntegerDigits[#], IntegerLength[#]} &, 82, 0] (* Michael De Vlieger, May 21 2021 *)
PROG
(PARI) a(n) = { my (d=digits(n)); sum (k=1, ceil(#d/2), d[k]*d[#d+1-k]) } \\ Rémy Sigrist, May 21 2021
CROSSREFS
KEYWORD
base,easy,nonn
AUTHOR
Amarnath Murthy, Aug 22 2005
EXTENSIONS
More terms from Joshua Zucker, May 08 2006
a(0) = 0 prepended and name clarified by Rémy Sigrist, May 21 2021
STATUS
approved