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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

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.

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

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Last modified July 20 12:40 EDT 2019. Contains 325180 sequences. (Running on oeis4.)