A321284 a(n) = 2*(2^(35*3^n) + 1).

68719476738, 81129638414606681695789005144066, 133499189745056880149688856635597007162669032647290798121690100488888732861290034376435130433538

Offset

0,1

Comments

Terms are a practical numbers.

a(3) has 285 digits.

Links

Table of n, a(n) for n=0..2.

Li-Yuan Wang and Zhi-Wei Sun, On practical numbers of some special forms, arXiv preprint arXiv:1809.01532 [math.NT], 2018.

Formula

a(n) = A005843(A000079(35*A000244(n)) + 1).

Maple

a := n -> 2*(2^(35*3^n)+1):
seq(a(n), n = 0 .. 5);

Mathematica

a[n_]:=2*(2^(35*3^n)+1); Array[a, 5, 0]

Prog

(GAP) Flat(List([0..2], n->List([0..n], k->2*(2^(35*3^k)+1))));
(Magma) [2*(2^(35*3^n)+1): n in [0..5]];
(Maxima) a(n):=2*(2^(35*3^n)+1)$ makelist(a(n), n, 0, 5);
(PARI) a(n)=2*(2^(35*3^n)+1);
tabl(nn) = for(n=0, nn, print1(a(n), ", "));
tabl(5)
(Python) for n in range(5): print(2 * (2**(35 * 3**n) + 1), end=', ')

Crossrefs

Cf. A005843, A000079, A000244, A005153 (practical number).

Subsequence of A321308.

Sequence in context: A017496 A017628 A139572 * A186095 A218397 A103617

Adjacent sequences: A321281 A321282 A321283 * A321285 A321286 A321287

Keyword

nonn

Author

Stefano Spezia, Nov 02 2018

Status

approved