Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 61st year, we have over 378,000 sequences, and we’ve reached 11,000 citations (which often say “discovered thanks to the OEIS”).
%I #23 Sep 19 2023 01:45:22
%S 5,7,11,49,13,77,17,343,121,91,19,539,23,119,143,2401,29,847,31,637,
%T 187,133,37,3773,169,161,1331,833,41,1001,43,16807,209,203,221,5929,
%U 47,217,253,4459,53,1309,59,931,1573,259,61,26411,289,1183,319,1127,67,9317,247
%N a(1)=5; for n >= 2, if n = Product p_i^e_i, then a(n) = Product p_{i+3}^e_i.
%D From a puzzle proposed by _Marc LeBrun_.
%e If n = 9 = 3^2, then a(n) = 11^2 = 121 (since 11 is the third prime after 3).
%t f[p_, e_] := NextPrime[p, 3]^e; a[1] = 5; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Sep 19 2023 *)
%Y Cf. A045965, A045966, A045967, A045969, A045970, A045971, A045972, A045973.
%K easy,nonn
%O 1,1
%A _N. J. A. Sloane_
%E More terms from _David W. Wilson_
%E Erroneous linear recurrence deleted by _Harvey P. Dale_, May 07 2018