A257999 - OEIS

The OEIS is supported by the many generous donors to the OEIS Foundation.

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”).

Other ways to Give

A257999

Numbers of the form, 2^i*3^j, i+j odd.

2, 3, 8, 12, 18, 27, 32, 48, 72, 108, 128, 162, 192, 243, 288, 432, 512, 648, 768, 972, 1152, 1458, 1728, 2048, 2187, 2592, 3072, 3888, 4608, 5832, 6912, 8192, 8748, 10368, 12288, 13122, 15552, 18432, 19683, 23328, 27648, 32768, 34992, 41472, 49152, 52488

(list; graph; refs; listen; history; text; internal format)

OFFSET

1,1

LINKS

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

A069352(a(n)) mod 2 = 1.

Sum_{n>=1} 1/a(n) = 5/4. - Amiram Eldar, Feb 18 2021

MATHEMATICA

max = 53000; Reap[Do[k = 2^i*3^j; If[k <= max && OddQ[i + j], Sow[k]], {i, 0, Log[2, max] // Ceiling}, {j, 0, Log[3, max] // Ceiling}]][[2, 1]] // Union (* Amiram Eldar, Feb 18 2021 after Jean-François Alcover at A036667 *)

PROG

(Haskell)

a257999 n = a257999_list !! (n-1)

a257999_list = filter (odd . flip mod 2 . a001222) a003586_list

CROSSREFS

Complement of A036667 with respect to A003586.

Intersection of A026424 and A003586.

Cf. A069352, A022328, A022329.

Sequence in context: A266629 A249096 A249367 * A350440 A115449 A303851

Adjacent sequences: A257996 A257997 A257998 * A258000 A258001 A258002

KEYWORD

nonn

AUTHOR

Reinhard Zumkeller, May 16 2015

STATUS

approved