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 A340636 Primes of the form k + A037276(k) in more than one way. 3

%I #13 Feb 06 2021 22:09:47

%S 251,2671,2687,2753,23327,23561,27827,28499,28789,28817,29411,34757,

%T 223441,226001,227537,230849,231359,232217,232259,232367,232643,

%U 232919,233591,234791,236129,236609,236867,237857,238141,239023,239873,240899,241169,241343,241687,241691,242447,242747,245299

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

%H Robert Israel, <a href="/A340636/b340636.txt">Table of n, a(n) for n = 1..7500</a>

%e a(3) = 2687 = 170 + A037276(170) = 170 + 2517

%e = 458 + A037276(458) = 458 + 2229.

%e The first term that occurs in more than two ways is

%e a(163) = 2255299 = 4180 + A037276(4180) = 4180 + 2251119

%e = 21156 + A037276(21156) = 21156 + 2234143

%e = 29560 + A037276(29560) = 29560 + 2225739.

%p N:= 5*10^5: # for terms <= N

%p dcat:= proc(L) local i, x;

%p x:= L[-1];

%p for i from nops(L)-1 to 1 by -1 do

%p x:= 10^(1+ilog10(x))*L[i]+x

%p od;

%p x

%p end proc:

%p A037276:= proc(n) local F;

%p F:= sort(ifactors(n)[2], (a, b) -> a[1] < b[1]);

%p dcat(map(t -> t[1]\$t[2], F));

%p end proc:

%p A037276(1):= 1:

%p R:= NULL:

%p for n from 1 to N/2 do

%p v:= n + A037276(n);

%p if v < N and isprime(v) then R:= R, v fi;

%p od:

%p S:= {R}:

%p select(s -> numboccur(s,[R])>1, S);

%Y Cf. A037276, A340633, A340634.

%K nonn,base

%O 1,1

%A _J. M. Bergot_ and _Robert Israel_, Jan 14 2021

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Last modified June 25 10:28 EDT 2024. Contains 373701 sequences. (Running on oeis4.)