

A085942


Write digit reversal of n below n. Then a(n) = the sum of the product of digits in the same column.


0



1, 4, 9, 16, 25, 36, 49, 64, 81, 0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 0, 6, 12, 18, 24, 30, 36, 42, 48, 54, 0, 8, 16, 24, 32, 40, 48, 56, 64, 72, 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 0, 12, 24, 36, 48, 60, 72, 84, 96, 108, 0, 14, 28, 42, 56, 70, 84
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OFFSET

1,2


COMMENTS

a(n) = sum of the products of rth most significant digit and the rth least significant digit, the sum being taken over all the digits of n.
If the number of digits in n is even then a(n) is also even.
a(36) = 36.


LINKS

Table of n, a(n) for n=1..76.


EXAMPLE

a(4) = 4*4 = 16.
a(123) = 10: 123
............ 321 (1*3 +2*2 +3*1 = 10).
a(1203) = 1*3 + 2*0 + 0*2 +3*1 = 6.
a(1234) = 1*4 +2*3 + 3*2 +4*1 = 20.


MATHEMATICA

dr[n_]:=Module[{idn=IntegerDigits[n]}, Total[Times@@@Transpose[Join[{idn, Reverse[idn]}]]]]; Array[dr, 80] (* Harvey P. Dale, May 03 2011 *)


CROSSREFS

Sequence in context: A169669 A111707 A115300 * A066308 A063462 A098736
Adjacent sequences: A085939 A085940 A085941 * A085943 A085944 A085945


KEYWORD

base,easy,nonn


AUTHOR

Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Jul 14 2003


EXTENSIONS

More terms from David Wasserman, Feb 14 2005
Edited by N. J. A. Sloane at the suggestion of Andrew S. Plewe, May 31 2007


STATUS

approved



