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Revision History for A191218

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A191218

Odd numbers n such that sigma(n) is congruent to 2 modulo 4.
(history; published version)

#26 by Charles R Greathouse IV at Wed Feb 16 23:10:44 EST 2022

STATUS

editing

approved

#25 by Charles R Greathouse IV at Wed Feb 16 23:10:39 EST 2022

PROG

(PARI) list(lim)=my(field=vectorsmall(lim\=1), v=List(), x2, t); for(x=2, sqrtint(lim-1), x2=x^2; t=sqrtint(lim-x2); forstep(ye=if(t<x, t-(x-t+1)%2, x-, logint(lim\=1, 5), 4, forprimestep(p=5, sqrtnint(lim, e), 1, -2, field[x2+y4, my(pe=p^2]++)e); forstep(nm=3, 1, sqrtint(lim), 2, field[n^2]=0\pe); for(n=, 2, lim, if(field[n]==1, m%p, listput(v, npe*m^2))))); field=0; VecSet(v) \\ Charles R Greathouse IV, Jan 06 2018Feb 16 2022

STATUS

approved

editing

#24 by Susanna Cuyler at Mon Apr 22 18:06:49 EDT 2019

STATUS

proposed

approved

#23 by Michel Marcus at Mon Apr 22 17:15:40 EDT 2019

STATUS

editing

proposed

#22 by Michel Marcus at Mon Apr 22 17:15:35 EDT 2019

PROG

(PARI) forstep(n=1, 10^3, 2, if(2==(sigma(n)%4), print1(n, ", "))) \\ _Joerg Arndt, _, May 27 2011

STATUS

proposed

editing

#21 by Antti Karttunen at Mon Apr 22 17:14:29 EDT 2019

STATUS

editing

proposed

#20 by Antti Karttunen at Mon Apr 22 17:14:15 EDT 2019

NAME

Odd numbers n such that sigma(n) is congruent to 2 modulo 4.

COMMENTS

See A228058 for a subset of the terms with where m > 1. - Antti Karttunen, Apr 22 2019

STATUS

proposed

editing

#19 by Antti Karttunen at Mon Apr 22 17:03:40 EDT 2019

STATUS

editing

proposed

#18 by Antti Karttunen at Mon Apr 22 17:02:14 EDT 2019

COMMENTS

See A228058 for a subset of terms with the additional criterion that m must be larger than > 1. - Antti Karttunen, Apr 22 2019

#17 by Antti Karttunen at Mon Apr 22 17:01:32 EDT 2019

COMMENTS

See A228058 for a subset of terms with the additional criterion that m must be larger than 1. - Antti Karttunen, Apr 22 2019

LINKS

Antti Karttunen, <a href="/A191218/b191218.txt">Table of n, a(n) for n = 1..20000</a>