A340636 Primes of the form k + A037276(k) in more than one way.

251, 2671, 2687, 2753, 23327, 23561, 27827, 28499, 28789, 28817, 29411, 34757, 223441, 226001, 227537, 230849, 231359, 232217, 232259, 232367, 232643, 232919, 233591, 234791, 236129, 236609, 236867, 237857, 238141, 239023, 239873, 240899, 241169, 241343, 241687, 241691, 242447, 242747, 245299

Offset

1,1

Links

Robert Israel, Table of n, a(n) for n = 1..7500

Example

a(3) = 2687 = 170 + A037276(170) = 170 + 2517
            = 458 + A037276(458) = 458 + 2229.
The first term that occurs in more than two ways is
a(163) = 2255299 =  4180 + A037276(4180)  =  4180 + 2251119
                 = 21156 + A037276(21156) = 21156 + 2234143
                 = 29560 + A037276(29560) = 29560 + 2225739.

Maple

N:= 5*10^5: # for terms <= N
dcat:= proc(L) local i, x;
  x:= L[-1];
  for i from nops(L)-1 to 1 by -1 do
    x:= 10^(1+ilog10(x))*L[i]+x
  od;
  x
end proc:
A037276:= proc(n) local F;
  F:= sort(ifactors(n)[2], (a, b) -> a[1] < b[1]);
  dcat(map(t -> t[1]$t[2], F));
end proc:
A037276(1):= 1:
R:= NULL:
for n from 1 to N/2 do
  v:= n + A037276(n);
  if v < N and isprime(v) then R:= R, v fi;
od:
S:= {R}:
select(s -> numboccur(s, [R])>1, S);

Crossrefs

Cf. A037276, A340633, A340634.

Sequence in context: A033451 A201793 A183840 * A234929 A218639 A090834

Adjacent sequences: A340633 A340634 A340635 * A340637 A340638 A340639

Keyword

nonn,base

Author

J. M. Bergot and Robert Israel, Jan 14 2021

Status

approved