|
|
|
|
2, 3, 7, 75, 86, 91, 1863, 2763, 3595, 5451, 6031, 7734, 8023, 9631, 35403, 41391, 53431, 63847, 64294, 148391, 205556, 237992, 374715, 381440, 404775, 442755, 510283, 546422, 917035, 1149111, 1291895, 1563158, 2197526, 2610182, 2693035, 2730524, 2804331, 3020715, 3547982, 4365950
(list;
graph;
refs;
listen;
history;
text;
internal format)
|
|
|
OFFSET
|
1,1
|
|
LINKS
|
|
|
MATHEMATICA
|
usigma[1] = 1; usigma[n_] := Times @@ (1 + Power @@@ FactorInteger[n]); seq = {}; u1 = usigma[1]; u2 = usigma[2]; Do[u3 = usigma[n]; If[u3 == 2*u2 - u1, AppendTo[seq, n - 2]]; u1 = u2; u2 = u3, {n, 3, 10^4}]; seq (* Amiram Eldar, Jan 04 2020 *)
|
|
PROG
|
(PARI) usigma(n) = sumdiv(n, d, if(gcd(d, n/d)==1, d));
lista(nn) = {u = vector(nn, n, usigma(n)); v = vector(#u-1, n, u[n+1] - u[n]); w = vector(#v-1, n, v[n+1] - v[n]); x = select(y->y==0, w, 1); } \\ Michel Marcus, Aug 12 2018
|
|
CROSSREFS
|
|
|
KEYWORD
|
nonn
|
|
AUTHOR
|
|
|
EXTENSIONS
|
|
|
STATUS
|
approved
|
|
|
|