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A321284
a(n) = 2*(2^(35*3^n) + 1).
0
68719476738, 81129638414606681695789005144066, 133499189745056880149688856635597007162669032647290798121690100488888732861290034376435130433538
OFFSET
0,1
COMMENTS
Terms are a practical numbers.
a(3) has 285 digits.
LINKS
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
KEYWORD
nonn
AUTHOR
Stefano Spezia, Nov 02 2018
STATUS
approved