A109162 a(1) = 1; for n > 1, a(n) = A019565(a(n-1)).

1, 2, 3, 6, 15, 210, 10659, 54230826, 249853434654335387610276087

Offset

1,2

Comments

After the initial 1, even-indexed terms are of the form 4k+2 (members of A016825) and odd-indexed terms are of the form 6k+3 (members of A016945). However, not all even terms after 2 are multiples of three, because not all odd-indexed terms are of the form 4k+3. For example, because a(11) is of the form 4k+1, a(12) cannot be a multiple of three. - Antti Karttunen, Jun 18 2017

Links

Frank Adams-Watters, Table of n, a(n) for n = 1..11

Example

a(4) = 6, which is 110 in binary. So a(5) is the product of the primes corresponding to the 1's of 110, 3*5 = 15.

Mathematica

NestList[Times @@ Prime@ Flatten@ Position[#, 1] &@ Reverse@ IntegerDigits[#, 2] &, 1, 11] (* Michael De Vlieger, Aug 20 2017 *)

Prog

(Scheme, with memoization-macro definec)
(definec (A109162 n) (if (zero? n) n (A019565 (A109162 (- n 1))))) ;; Antti Karttunen, Jun 18 2017

Crossrefs

Cf. A019565, A285320 (a left inverse).

The left edge of A285332 and A285333.

Sequence in context: A014627 A145781 A351880 * A215659 A028688 A342027

Adjacent sequences: A109159 A109160 A109161 * A109163 A109164 A109165

Keyword

nonn

Author

Leroy Quet, Aug 18 2005

Extensions

More terms from Franklin T. Adams-Watters, Aug 29 2006

Status

approved