A258125 a(1) = a(2) = 2; a(n) = a(n-1) + gpf(a(n-2)), where gpf is greatest prime factor.

2, 2, 4, 6, 8, 11, 13, 24, 37, 40, 77, 82, 93, 134, 165, 232, 243, 272, 275, 292, 303, 376, 477, 524, 577, 708, 1285, 1344, 1601, 1608, 3209, 3276, 6485, 6498, 7795, 7814, 9373, 13280, 13383, 13466, 14953, 21686, 22473, 24022, 24249, 36260

Offset

1,1

Links

Anders Hellström, Table of n, a(n) for n = 1..1000

Mathematica

a[1] = a[2] = 2; a[n_] := a[n] = a[n - 1] + FactorInteger[a[n - 2]][[-1, 1]]; Table[a@ n, {n, 46}] (* Michael De Vlieger, Nov 16 2015 *)
nxt[{a_, b_}]:={b, b+FactorInteger[a][[-1, 1]]}; Transpose[NestList[nxt, {2, 2}, 50]][[1]] (* Harvey P. Dale, Nov 22 2015 *)

Prog

(PARI) gpf(n)=my(f=factor(n)[, 1]); f[#f];
first(m)=my(v=vector(m)); v[1]=2; v[2]=2; for(i=3, m, v[i]=v[i-1]+gpf(v[i-2])); v
(Haskell)
a258125 n = a258125_list !! (n-1)
a258125_list = 2 : 2 : zipWith (+)
               (map a006530 a258125_list) (tail a258125_list)
-- Reinhard Zumkeller, Nov 17 2015

Crossrefs

Cf. A006530 (gpf), A078695 (same recurrence).

Sequence in context: A179999 A286736 A241383 * A361394 A147982 A329899

Adjacent sequences: A258122 A258123 A258124 * A258126 A258127 A258128

Keyword

nonn

Author

Anders Hellström, Nov 16 2015

Status

approved