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a(n) = first digit to the right of decimal point of n*(sqrt(5)-1)/2.
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%I #4 Feb 11 2024 22:58:44

%S 6,2,8,4,0,7,3,9,5,1,7,4,0,6,2,8,5,1,7,3,9,5,2,8,4,0,6,3,9,5,1,7,3,0,

%T 6,2,8,4,1,7,3,9,5,1,8,4,0,6,2,9,5,1,7,3,9

%N a(n) = first digit to the right of decimal point of n*(sqrt(5)-1)/2.

%D J. Kappraff, Beyond Measure, World Scientific, 2002, p. 537.

%F n*0.618033989..., discard integer, then extract first digit to right of decimal.

%e 12th term is 4 since (12)(.618033989...) = 7.4164...

%o (PARI) a(n)=(sqrtint(125*n^2)-n%2*5)%10 \\ _Charles R Greathouse IV_, Feb 11 2024

%K nonn,base,easy

%O 1,1

%A _Gary W. Adamson_, May 07 2003