OFFSET
1,1
COMMENTS
a(n) >= A309906(3) = 8 for n > 3.
EXAMPLE
p = factorization
n prime(n) p^3 - 1 of p^3 - 1 a(n)
-- -------- ------- ----------------------- ----
1 2 7 7 2
2 3 26 2 * 13 4
3 5 124 2^2 * 31 6
4 7 342 2 * 3^2 * 19 12
5 11 1330 2 * 5 * 7 * 19 16
6 13 2196 2^2 * 3^2 * 61 18
7 17 4912 2^4 * 307 10
8 19 6858 2 * 3^3 * 127 16
9 23 12166 2 * 7 * 11 * 79 16
10 29 24388 2^2 * 7 * 13 * 67 24
11 31 29790 2 * 3^2 * 5 * 331 24
12 37 50652 2^2 * 3^3 * 7 * 67 48
13 41 68920 2^3 * 5 * 1723 16
14 43 79506 2 * 3^2 * 7 * 631 24
15 47 103822 2 * 23 * 37 * 61 16
16 53 148876 2^2 * 7 * 13 * 409 24
17 59 205378 2 * 29 * 3541 8
18 61 226980 2^2 * 3^2 * 5 * 13 * 97 72
19 67 300762 2 * 3^2 * 7^2 * 11 * 31 72
20 71 357910 2 * 5 * 7 * 5113 16
MATHEMATICA
a[n_] := DivisorSigma[0, Prime[n]^3 - 1]; Array[a, 50] (* Amiram Eldar, Feb 26 2021 *)
PROG
(PARI) a(n) = numdiv(prime(n)^3-1); \\ Michel Marcus, Feb 26 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Jon E. Schoenfield, Feb 26 2021
STATUS
approved