A097978 - OEIS

%I #17 Mar 01 2017 12:47:44

%S 1,2,33,102,1326,115005,31295895,159282123,9617162170,1535531452026,

%T 1960347077019695,16513791577659519,271518698440871310

%N a(n) = least m such that m and m+n are both products of exactly n distinct primes.

%C Note that a(n) and a(n)+n are required to be squarefree (compare A135058). - _David Wasserman_, Feb 19 2008

%C If we change "exactly n" to "at least n", the sequence is still the same at least through a(12). - _David Wasserman_, Feb 19 2008

%C a(13) <= 592357638037885411965. - _David Wasserman_, Feb 19 2008

%F a(n) = min{m: A001221(m) = A001222(m) = A001221(m+n) = A001222(m+n)= n}. - _R. J. Mathar_, Mar 01 2017

%e a(2) = 33  because 33 and 35 are both in A006881.

%e a(3) = 102 because 102 and 105 are both in A007304.

%e a(4) = 1326 because 1326 and 1330 are both in A046386.

%t f[n_] := Block[{lst = FactorInteger[n], a, b}, a = Plus @@ Last /@ lst; b = Length[lst]; If[a == b, b, 0]]; g[n_] := Block[{k = Product[ Prime[i], {i, n}]}, While[ f[k] != n || f[k] != f[k + n], k++ ]; k]; Do[ Print[ g[n]], {n, 1, 6}] (* _Robert G. Wilson v_, Sep 11 2004 *)

%Y Cf. A098515. A135058 (without regard to multiplicity).

%K more,nonn

%O 0,2

%A _Lekraj Beedassy_, Sep 07 2004

%E Edited and extended by Mark Hudson (mrmarkhudson(AT)hotmail.com), Sep 08 2004

%E More terms from _David Wasserman_, Feb 19 2008