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A085942
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Write digit reversal of n below n. Then a(n) = the sum of the product of digits in the same column.
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0
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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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| a(n) = sum of the products of r-th most significant digit and the r-th 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.
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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.
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MATHEMATICA
| dr[n_]:=Module[{idn=IntegerDigits[n]}, Total[Times@@@Transpose[Join[{idn, Reverse[idn]}]]]]; Array[dr, 80] (* From Harvey P. Dale, May 03 2011 *)
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CROSSREFS
| Sequence in context: A169669 A111707 A115300 * A066308 A063462 A098736
Adjacent sequences: A085939 A085940 A085941 * A085943 A085944 A085945
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KEYWORD
| base,easy,nonn
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AUTHOR
| Amarnath Murthy and Meenakshi Srikanth (amarnath_murthy(AT)yahoo.com), Jul 14 2003
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EXTENSIONS
| More terms from David Wasserman (wasserma(AT)spawar.navy.mil), Feb 14 2005
Edited by N. J. A. Sloane (njas(AT)research.att.com) at the suggestion of Andrew Plewe, May 31 2007
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