A089787 - OEIS

A089787

a(4n-3), a(4n-2), a(4n-1), and a(4n) are the units digit of the n-th prime followed by 1, 3, 7, and 9 respectively.

21, 23, 27, 29, 31, 33, 37, 39, 51, 53, 57, 59, 71, 73, 77, 79, 11, 13, 17, 19, 31, 33, 37, 39, 71, 73, 77, 79, 91, 93, 97, 99, 31, 33, 37, 39, 91, 93, 97, 99, 11, 13, 17, 19, 71, 73, 77, 79, 11, 13, 17, 19, 31, 33, 37, 39, 71, 73, 77, 79, 31, 33, 37, 39, 91, 93, 97, 99, 11

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OFFSET

1,1

LINKS

Harvey P. Dale, Table of n, a(n) for n = 1..1000

FORMULA

a(n) = 5+(-1)^n+3*cos(n*Pi/2)-3*sin(n*Pi/2)+10*(prime(floor((n+3)/4)) mod 10). - Wesley Ivan Hurt, May 06 2021

MATHEMATICA

Flatten[Table[Mod[Prime[n], 10]*10+{1, 3, 7, 9}, {n, 1, 50}]]

a[n_] := Mod[Prime[Floor[(n + 3)/4]], 10]*10 + {1, 3, 7,

9}[[Mod[n - 1, 4] + 1]] (* Charles R Greathouse IV, Jan 02 2013 *)

Table[10*Mod[Prime[n], 10]+{1, 3, 7, 9}, {n, 30}]//Flatten (* Harvey P. Dale, Aug 24 2019 *)