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A340636 Primes of the form k + A037276(k) in more than one way. 3
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,1
LINKS
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
Sequence in context: A033451 A201793 A183840 * A234929 A218639 A090834
KEYWORD
nonn,base
AUTHOR
J. M. Bergot and Robert Israel, Jan 14 2021
STATUS
approved

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Last modified May 26 16:43 EDT 2024. Contains 372840 sequences. (Running on oeis4.)