A111386 a(1) = 1, a(2) = 3; for n >= 3, take a(n) to be the smallest odd number not occurring earlier such that a(n-1) divides the concatenation a(n-2)a(n).

1, 3, 5, 15, 25, 75, 125, 375, 625, 1875, 3125, 9375, 15625, 46875, 78125, 234375, 390625, 1171875, 1953125, 5859375, 9765625, 29296875, 48828125, 146484375, 244140625, 732421875, 1220703125, 3662109375, 6103515625, 18310546875, 30517578125

Offset

1,2

Comments

Apparently identical to A056487. Is this a theorem? - Klaus Brockhaus, Jul 21 2009

Brockhaus' observation is true (see Fried link). - Sela Fried, Feb 24 2026

Links

Table of n, a(n) for n=1..31.

Sela Fried, Proof of a conjecture stated in A056487 and A111386, 2026.

Example

After 75 the term is 125 since 75 divides 25125.

Crossrefs

Cf. A111387.

Sequence in context: A328834 A018421 A163114 * A056487 A146582 A349967

Adjacent sequences: A111383 A111384 A111385 * A111387 A111388 A111389

Keyword

base,nonn

Author

Amarnath Murthy, Nov 11 2005

Extensions

More terms from R. J. Mathar, Aug 20 2007

a(21)-a(31) from Donovan Johnson, Apr 27 2008

Status

approved