A305718 a(n) is the smallest number k such that sigma(k + 2n) = sigma(k) - 2n, or -1 if no such number exists.

1, 6976, 15, 35, 39, 51, 95, 831, 45, 88, 63, 222, 135, 37888, 96, 284, 117, 354, 175, 84, 153, 176, 3893, 267, 210

Offset

0,2

Comments

Even-indexed terms of A304994.

If it exists, a(25) > 10^9. Other large (if existent) terms include a(55), a(73), and a(97).

Terms a(26)..a(54) are 120, 160, 228, 339, 602, 156, 1393, 425, 279, 1204, 462, 70912, 231, 488, 633, 1099, 575, 228, 369, 1211, 387, 364, 605, 579, 396, 725, 1731, 1146, 455.

a(25) > 10^12, if it exists. - Giovanni Resta, Jun 10 2018

Links

Table of n, a(n) for n=0..24.

Formula

a(n) = A304994(2n).

Crossrefs

Cf. A304994.

Sequence in context: A234111 A184228 A050225 * A237237 A251651 A050673

Adjacent sequences: A305715 A305716 A305717 * A305719 A305720 A305721

Keyword

nonn,more

Author

Jon E. Schoenfield, Jun 08 2018

Status

approved