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

Author

Jon E. Schoenfield, Jun 08 2018

Keywords

• nonn
• more

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

Crossrefs

Cf. A304994.

Formula

a(n) = A304994(2n).