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A175956 Numbers n such that A109925(n) = A109925(n+1).

%I A175956 #15 Oct 21 2024 12:30:31
%S A175956 1,6,29,41,53,59,65,89,97,126,137,148,163,179,191,192,193,223,233,239,
%T A175956 250,252,257,269,281,307,311,330,336,359,372,389,402,419,431,457,491,
%U A175956 504,508,521,547,557,569,598,613,641,653,659,673,683,700,719,733,739
%N A175956 Numbers n such that A109925(n) = A109925(n+1).
%C A175956 (Number of primes of the form n-2^k) = (number of primes of the form n-2^k+1).
%H A175956 Muniru A Asiru, <a href="/A175956/b175956.txt">Table of n, a(n) for n = 1..332</a>
%F A175956 A109925(a(n)) = A109925(a(n) + 1).
%e A175956 a(2)=6 because A109925(6) = A109925(7) = 2.
%p A175956 A109925 := proc(n) a := 0 ; for k from 0 do p := n-2^k ; if p < 2 then return a; elif isprime(p) then a := a+1 ; end if; end do: end proc:
%p A175956 isA175956 := proc(n) A109925(n) = A109925(n+1) ; end proc:
%p A175956 for n from 1 to 1500 do if isA175956(n) then printf("%d,",n); end if; end do:
%p A175956 # _R. J. Mathar_, Oct 30 2010
%t A175956 SequencePosition[Table[Count[n-2^Range[0,Floor[Log2[n]]],_?PrimeQ],{n,800}],{x_,x_}][[;;,1]] (* _Harvey P. Dale_, Oct 21 2024 *)
%o A175956 (Magma) a109925:=function(n); count:=0; e:=1; while e le n do if IsPrime(n-e) then count+:=1; end if; e*:=2; end while; return count; end function; S:=[]; a:=a109925(1); for n in [1..750] do b:=a109925(n+1); if a eq b then Append(~S, n); end if; a:=b; end for; S; // _Klaus Brockhaus_, Oct 30 2010
%Y A175956 Cf. A000040, A000079.
%K A175956 nonn
%O A175956 1,2
%A A175956 _Juri-Stepan Gerasimov_, Oct 29 2010, Oct 31 2010
%E A175956 More terms from _Klaus Brockhaus_ and _R. J. Mathar_, Oct 30 2010