login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A249410 Primes p such that sigma(p-1) is odd. 1
2, 3, 5, 17, 19, 37, 73, 101, 163, 197, 257, 401, 577, 677, 883, 1153, 1297, 1459, 1601, 1801, 2179, 2593, 2917, 3137, 3529, 4051, 4357, 5477, 7057, 8101, 8713, 8837, 10369, 11251, 12101, 13457, 14401, 15139, 15377, 15877, 16901, 17299, 17957, 18433, 19603 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Subsequence of A058501.

Union of A002496 and A090698. - Ivan Neretin, Dec 04 2018

LINKS

Charles R Greathouse IV, Table of n, a(n) for n = 1..10000

EXAMPLE

2 is in this sequence because 2 is prime and sigma(2-1) = 1 is odd.

MATHEMATICA

Select[Range[20000], PrimeQ[#] && OddQ[DivisorSigma[1, #-1]] &] (* Amiram Eldar, Dec 04 2018 *)

PROG

(PARI) lista(nn) = {forprime(p=2, nn, if (sigma(p-1) % 2, print1(p, ", ")); ); } \\ Michel Marcus, Oct 30 2014

(PARI) list(lim)=my(v=List([2]), t); forstep(n=2, sqrt(lim), 2, if(isprime(t=n^2+1), listput(v, t))); for(n=1, sqrtint(lim\2), if(isprime(t=2*n^2+1), listput(v, t))); Set(v) \\ Charles R Greathouse IV, Nov 04 2014

(GAP) Filtered(Filtered([1..25000], i->IsPrime(i)), p->IsOddInt(Sigma(p-1))); # Muniru A Asiru, Dec 05 2018

CROSSREFS

Cf. A000203, A058501, A090698.

Sequence in context: A290043 A058501 A215356 * A119405 A032733 A111632

Adjacent sequences:  A249407 A249408 A249409 * A249411 A249412 A249413

KEYWORD

nonn

AUTHOR

Juri-Stepan Gerasimov, Oct 27 2014

EXTENSIONS

More terms from Michel Marcus, Oct 30 2014

STATUS

approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified October 19 15:29 EDT 2021. Contains 348091 sequences. (Running on oeis4.)