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

 

Logo

Year-end appeal: Please make a donation to the OEIS Foundation to support ongoing development and maintenance of the OEIS. We are now in our 56th year, we are closing in on 350,000 sequences, and we’ve crossed 9,700 citations (which often say “discovered thanks to the OEIS”).

Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A345316 a(n) is the first number k such that there are exactly n primes of the form k + A - B where A and B are sums of subsets of the prime factors of k. 1
1, 2, 39, 20, 6, 10, 105, 285, 165, 615, 570, 1482, 1596, 2706, 3885, 14790, 19470, 24090, 19425, 33630, 33558, 80178, 134178, 115878, 151662, 428090, 418938, 631470, 672105, 1366530, 1006278, 1461570, 1155990, 1718310, 2382510, 3344430, 3669090, 4441530, 4562922, 3545178, 6087030, 7945230 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..41.

FORMULA

A345300(a(n)) = n.

EXAMPLE

a(3) = 20 because there are exactly 3 primes of this form for k=20, namely 13 = 20-2-5, 17 = 20+2-5, and 23 = 20+5-2, and this is the least number for which there are exactly 3 such primes.

MAPLE

f:= proc(n) local S, p;

  S:= {n};

  for p in numtheory:-factorset(n) do

    S:= S union map(`+`, S, p) union map(`-`, S, p)

  od:

  nops(select(isprime, S))

end proc:

V:= Array(0..30): count:= 0:

for n from 1 while count < 31 do

v:= f(n);

if v <= 30 and V[v] = 0 then count:= count+1; V[v]:= n fi

od:

convert(V, list);

CROSSREFS

Cf. A345300.

Sequence in context: A263374 A066244 A055689 * A028442 A062982 A042801

Adjacent sequences:  A345313 A345314 A345315 * A345317 A345318 A345319

KEYWORD

nonn

AUTHOR

J. M. Bergot and Robert Israel, Jun 13 2021

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 December 7 15:24 EST 2021. Contains 349581 sequences. (Running on oeis4.)