A083119 Sum of n terms from the n-th term is a square: a(1), a(2) + a(3), a(3) + a(4) + a(5),..., a(n) + a(n+1) + ...+ a(2n-1) are squares.

1, 2, 7, 3, 6, 4, 12, 5, 9, 8, 11, 10, 26, 13, 18, 14, 35, 15, 19, 16, 48, 17, 25, 20, 23, 21, 40, 22, 28, 24, 33, 27, 71, 29, 51, 30, 32, 31, 37, 34, 86, 36, 67, 38, 95, 39, 47, 41, 42, 43, 45, 44, 113, 46, 65, 49, 121, 50, 55, 52, 132, 53, 63, 54, 58

Offset

1,2

Comments

a(2n) is the smallest number that has not occurred earlier and a(2n+1) is the smallest number (again not included earlier) required to satisfy the requirement. Another permutation of natural numbers.

Links

Table of n, a(n) for n=1..65.

Prog

(GAP) sq := List([1..100], x->x^2); l := [1]; k := 2;
repeat m := Minimum(Difference([1..Size(l)+1], l)); Add(l, m);
sum := Sum(List([k..2*k-2], x->l[x]));
m := sq[PositionProperty(sq, x->x>sum and not x-sum in l)]-sum;
Add(l, m); k := k+1;
until k = 50; l; - Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jun 29 2005

Crossrefs

Cf. A083121.

Sequence in context: A104957 A329333 A377483 * A246163 A198388 A334375

Adjacent sequences: A083116 A083117 A083118 * A083120 A083121 A083122

Keyword

nonn

Author

Amarnath Murthy and Meenakshi Srikanth (menakan_s(AT)yahoo.com), Apr 23 2003

Extensions

More terms from Simon Nickerson (simonn(AT)maths.bham.ac.uk), Jun 29 2005

Status

approved