A391881 a(n) = T(n,1) + T(n,n), where T(n,k) is A391880.

4, 5, 10, 18, 37462, 24, 1367566, 60, 196607854, 60, 120670499918, 330, 2339539498438, 16043622, 7891538081398078, 2142130380, 318135617703221314, 3227805300, 13839880244194493194, 3595191630030

Offset

1,1

Links

Table of n, a(n) for n=1..20.

Example

a(1): [2] + [2] = [4];
a(2): [2,3] + [3,2] = [5,5];
a(3): [3,5,7] + [7,5,3] = [10,10,10];
a(4): [5,7,11,13] + [13,11,7,5] = [18,18,18,18];
a(5): [18713,18719,18731,18743,18749] + [18749,18743,18731,18719,18713] = [37462,37462,37462,37462,37462];
a(8): [17,19,23,29,31,37,41,43] + [43,41,...,19,17] = [60,60,...,60,60];
a(10): [13,17,19,23,29,31,37,41,43,47] + [47,43,...,17,13] = [60,60,...,60,60].

Crossrefs

Cf. A175309, A391880.

Sequence in context: A049897 A049867 A054173 * A185875 A393602 A354080

Adjacent sequences: A391878 A391879 A391880 * A391882 A391883 A391884

Keyword

nonn,more,hard

Author

Hugo Pfoertner, Dec 22 2025

Status

approved