OFFSET
1,2
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
The prime signatures of the first 12 terms are:
-- ------- ------------ ------------- -------------
1 1 {} 0 0
2 60 {1,1,2} 2 1+1=2
3 2160 {1,3,4} 4 1+3=4
4 12600 {1,2,2,3} 2+2=4 1+3=4
5 18480 {1,1,1,1,4} 4 1+1+1+1=4
6 77760 {1,5,6} 6 1+5=6
7 180180 {1,1,1,1,2,2} 2+2=4 1+1+1+1=4
8 216000 {3,3,6} 6 3+3=6
9 453600 {1,2,4,5} 2+4=6 1+5=6
10 665280 {1,1,1,3,6} 6 1+1+1+3=6
11 2646000 {2,3,3,4} 2+4=6 3+3=6
12 2799360 {1,7,8} 8 1+7=8
MATHEMATICA
fun[p_, e_] := (-1)^e * e; q[n_] := Module[{f = FactorInteger[n]}, n == 1 || (f[[-1, 1]] == Prime[Length[f]] && Plus @@ fun @@@ f == 0 && Max@ Differences[f[[;; , 2]]] < 1)]; Select[Range[4*10^6], q]
PROG
(PARI) is(n) = {my(f = factor(n), p = f[, 1], e = f[, 2]); n == 1 || (sum(i = 1, #e, (-1)^e[i] * e[i]) == 0 && e == vecsort(e, , 4) && primepi(p[#p]) == #p); }
CROSSREFS
KEYWORD
nonn
AUTHOR
Amiram Eldar, Mar 29 2024
STATUS
approved