login

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).

a(n) = n-th decimal digit of the fractional part of the cube root of the n-th prime.
1

%I #20 Feb 22 2024 13:32:54

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

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

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

%N a(n) = n-th decimal digit of the fractional part of the cube root of the n-th prime.

%D John D. Barrow, The Infinite Book, Pantheon Book New York 2005, pp. 69-76.

%e The 2nd prime is 3. 3^(1/3) = 1.442249..., The 2nd entry after the decimal point is 4 the 2nd entry in the table.

%t a[n_] := Block[{rd = RealDigits[(Prime@n)^(1/3), 10, 111]}, rd[[1, n + rd[[2]]]]];

%t Array[a, 105] (* _Robert G. Wilson v_, Nov 17 2005 *)

%o (PARI) a(n) = localprec(n+1); floor(frac(sqrtn(prime(n), 3))*10^n) % 10; \\ _Michel Marcus_, Feb 22 2024

%Y Cf. A071901.

%K easy,nonn,base

%O 2,1

%A _Cino Hilliard_, Nov 13 2005

%E More terms from _Robert G. Wilson v_, Nov 17 2005