A246637 Integers of the form (2^(k+1) - 1)/C(k+2,2).

1, 1, 3, 1533, 4870483401, 10632494904416274948861848751148863, 442778652527729430645666843207235634221292901, 8594831104112238244501123836952492157088005557663896974587707618787108, 970692073484990407927190417652798419153

Offset

1,3

Comments

The numbers k for which (2^(k+1) - 1)/C(k+2,2) is an integer are given by A246636. For each such k, (2^(k+1) - 1)/C(k+2,2) is the mean of the numbers in all the rows of Pascal's triangle, from row 0 through row k.

Links

Table of n, a(n) for n=1..9.

Example

The sum of the numbers in Pascal's triangle, from row 0 through row 17, is 2^18 - 1 = 262143; the number of such numbers is C(19,2) = 171, and 262143/171 = 1533; thus is in A246637 and 17 is in A246636.

Mathematica

z = 3000; t = Select[Range[0, z], IntegerQ[(2^(# + 1) - 1)/Binomial[# + 2, 2]] &] (* A246636 *)
Table[(2^(t[[n]] + 1) - 1)/Binomial[t[[n]] + 2, 2], {n, 1, 10}]  (*A246637*)

Crossrefs

Cf. A246636, A007318.

Sequence in context: A285656 A239503 A118050 * A302132 A346653 A258720

Adjacent sequences: A246634 A246635 A246636 * A246638 A246639 A246640

Keyword

nonn,easy

Author

Clark Kimberling, Sep 01 2014

Status

approved