A251618 Smallest term in A098550 having prime(n) as a factor.

2, 3, 15, 14, 22, 39, 51, 38, 69, 87, 62, 74, 123, 86, 94, 106, 118, 122, 201, 142, 146, 158, 249, 178, 291, 202, 206, 214, 218, 226, 254, 262, 274, 278, 298, 302, 314, 326, 334, 346, 358, 362, 382, 386, 394, 398, 422, 446, 454, 458, 466, 478, 482, 502, 514

Offset: 1

Author

Reinhard Zumkeller, Dec 07 2014

Keywords

• nonn

Comments

Largest prime factor of a(n) = prime(n);

a(n) is composite for n > 2;

first column in A251637;

conjecture: for n > 2: a(n) = 2*prime(n) or a(n) = 3*prime(n);

conjecture: for n > 25: a(n) = 2*prime(n).

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A098550, A000040, A251637, A251619 (smallest prime factor), A006530.

Programs

Haskell

import Data.List (find); import Data.Maybe (fromJust)
a251618 n = fromJust $
            find (\x -> mod x (fromIntegral $ a000040 n) == 0) a098550_list

Mathematica

nmax = 100;
b[n_] := b[n] = If[n <= 4, n, For[k = 1, True, k++, If[FreeQ[Array[b, n-1], k] && GCD[k, b[n-1]] == 1 && GCD[k, b[n-2]] > 1, Return[k]]]];
A098550 = Array[b, 12*nmax]; (* If the message Missing[NotFound] appears, the coefficient 12 in 12*nmax should be increased. *)
a[n_] := SelectFirst[A098550, Divisible[#, Prime[n]]&];
Table[a[n], {n, 1, nmax}] (* Jean-François Alcover, Sep 27 2021 *)