A062094 - OEIS

A062094

a(1) = 2, a(n) = concatenation of two closest factors of a(n-1) whose product equals a(n-1) or if a(n-1) is a prime then the concatenation of 1 and a(n-1).

%I #6 Mar 20 2023 22:57:29

%S 2,12,34,217,731,1743,2183,3759,21179,121179,931303,1931303,11175573,

%T 11379829,17896361,18419721,96919009,889910891,1889910891,2742368917,

%U 25741106537,110203233579,679231622473,1679231622473,7921256096487

%N a(1) = 2, a(n) = concatenation of two closest factors of a(n-1) whose product equals a(n-1) or if a(n-1) is a prime then the concatenation of 1 and a(n-1).

%H Sean A. Irvine, <a href="/A062094/b062094.txt">Table of n, a(n) for n = 1..250</a>

%e a(1) = 2 is a prime hence a(2) = 12; a(3) = 34, 3*4 = 12 and 3<4.

%t f[n_Integer] := (d = Divisors[n]; l = Length[d]; If[ EvenQ[l], ToExpression[ ToString[ d[[l/2]] ] <> ToString[ d[[l/2 + 1]] ]], ToExpression[ ToString[d[[l/2 + .5]] ] <> ToString[ d[[l/2 + .5]] ]]] ); NestList[f, 2, 25]

%Y Cf. A003681, A062095.

%K nonn,easy,base

%O 1,1

%A _Amarnath Murthy_, Jun 16 2001

%E More terms from _Robert G. Wilson v_, Aug 08 2001