A045968 a(1)=5; for n >= 2, if n = Product p_i^e_i, then a(n) = Product p_{i+3}^e_i.

5, 7, 11, 49, 13, 77, 17, 343, 121, 91, 19, 539, 23, 119, 143, 2401, 29, 847, 31, 637, 187, 133, 37, 3773, 169, 161, 1331, 833, 41, 1001, 43, 16807, 209, 203, 221, 5929, 47, 217, 253, 4459, 53, 1309, 59, 931, 1573, 259, 61, 26411, 289, 1183, 319, 1127, 67, 9317, 247

Offset: 1

Author

N. J. A. Sloane

Keywords

• easy
• nonn

Examples

			If n = 9 = 3^2, then a(n) = 11^2 = 121 (since 11 is the third prime after 3).
		

References

• From a puzzle proposed by Marc LeBrun.

Crossrefs

Cf. A045965, A045966, A045967, A045969, A045970, A045971, A045972, A045973.

Programs

Mathematica

f[p_, e_] := NextPrime[p, 3]^e; a[1] = 5; a[n_] := Times @@ f @@@ FactorInteger[n]; Array[a, 100] (* Amiram Eldar, Sep 19 2023 *)

Extensions

More terms from David W. Wilson

Erroneous linear recurrence deleted by Harvey P. Dale, May 07 2018