The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A337878 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A337878

a(n) is the smallest m > 0 such that the n-th prime divides Jacobsthal(m).
(history; published version)

#27 by N. J. A. Sloane at Mon Oct 05 01:05:42 EDT 2020

STATUS

proposed

approved

#26 by Michel Marcus at Wed Sep 30 00:58:08 EDT 2020

STATUS

editing

proposed

#25 by Michel Marcus at Wed Sep 30 00:57:58 EDT 2020

PROG

a(n) = {my(k=1, p=prime(n)); while (J(k) % p, k++); k; } \\ Michel Marcus, Sep 29 2020

STATUS

proposed

editing

#24 by Michel Marcus at Tue Sep 29 23:52:34 EDT 2020

STATUS

editing

proposed

#23 by Michel Marcus at Tue Sep 29 23:40:32 EDT 2020

PROG

(PARI) J(n) = (2^n - (-1)^n)/3; \\ A001045

a(n) = {my(k=1, p=prime(n)); while (J(k) % p, k++); k; \\ Michel Marcus, Sep 29 2020

STATUS

proposed

editing

#22 by A.H.M. Smeets at Tue Sep 29 20:08:16 EDT 2020

STATUS

editing

proposed

Discussion

Tue Sep 29

20:13

A.H.M. Smeets: Thanks David and Omar.

#21 by A.H.M. Smeets at Tue Sep 29 20:07:31 EDT 2020

EXAMPLE

The 4th prime number is 7, and 7 divides 21 which is Jacobsthal(6), so a(4) = 6. The second prime number, 3, divides Jacobsthal(6) as well, but it divides also the smaller Jacobsthal(3), i.e., a(2) = 3.

STATUS

proposed

editing

#20 by Omar E. Pol at Mon Sep 28 13:23:17 EDT 2020

STATUS

editing

proposed

#19 by Omar E. Pol at Mon Sep 28 13:22:23 EDT 2020

NAME

Jacobsthal entry points: a(n) is the smallest m > 0 such that the n-th prime divides Jacobsthal(m).

STATUS

proposed

editing

Discussion

Mon Sep 28

13:23

Omar E. Pol: Removed the first part of the definition which is not necessary.

#18 by Amiram Eldar at Mon Sep 28 13:06:31 EDT 2020

STATUS

editing

proposed