The On-Line Encyclopedia of Integer Sequences (OEIS)

Revision History for A154729 (Bold, blue-underlined text is an addition; faded, red-underlined text is a ~~deletion~~.)
Showing entries 1-10 | older changes

A154729

Products of three distinct primes of the form 6*k + 1.
(history; published version)

#26 by Susanna Cuyler at Tue Jul 20 11:34:38 EDT 2021

STATUS

proposed

approved

#25 by Omar E. Pol at Sun Jul 18 16:18:11 EDT 2021

STATUS

editing

proposed

#24 by Omar E. Pol at Sun Jul 18 16:18:07 EDT 2021

COMMENTS

Note that a(1) = 1729 is the Hardy-Ramanujan number (see taxicab numbers in A001235, A011541).

STATUS

proposed

editing

#23 by Felix Fröhlich at Wed Jul 07 14:03:37 EDT 2021

STATUS

editing

proposed

Discussion

Wed Jul 07

14:22

Omar E. Pol: Thanks!

#22 by Felix Fröhlich at Wed Jul 07 14:02:04 EDT 2021

LINKS

Felix Fröhlich, <a href="/A154729/b154729.txt">Table of n, a(n) for n = 1..10000</a>

#21 by Felix Fröhlich at Wed Jul 07 13:56:48 EDT 2021

PROG

(PARI) fct(n, o=[1])=if(n>1, concat(apply(t->vector(t[2], i, t[1]), Vec(factor(n)~))), o) \\ after M. F. Hasler in A027746

is(n) = my(f=fct(n)); if(#f!=3 || f!=vecsort(f, , 8), return(0), for(k=1, #f, if((f[k]-1)/6!=ceil((f[k]-1)/6), return(0)))); 1 \\ Felix Fröhlich, Jul 07 2021

#20 by Felix Fröhlich at Wed Jul 07 13:41:47 EDT 2021

NAME

Products of three distinct primes of the form 6*n k + 1.

COMMENTS

Equivalently, products of three distinct primes of the form 3*n k + 1. - Omar E. Pol, Feb 17 2018

EXAMPLE

The first three primes of the form 6*n k + 1 are 7, 13 and 19, so a(1) = 7*13*19 = 1729. - Omar E. Pol, Feb 17 2018

STATUS

proposed

editing

Discussion

Wed Jul 07

13:43

Felix Fröhlich: Replaced instances of "n" by "k".

#19 by Omar E. Pol at Tue Jul 06 18:25:57 EDT 2021

STATUS

editing

proposed

#18 by Omar E. Pol at Tue Jul 06 18:25:45 EDT 2021

NAME

Products of three distinct primes of the form 6*n + 1 (see A002476).

CROSSREFS

Subsequence of A007304.

STATUS

approved

editing

#17 by Peter Luschny at Tue Feb 20 11:54:56 EST 2018

STATUS

reviewed

approved