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

1, 6, 29, 41, 53, 59, 65, 89, 97, 126, 137, 148, 163, 179, 191, 192, 193, 223, 233, 239, 250, 252, 257, 269, 281, 307, 311, 330, 336, 359, 372, 389, 402, 419, 431, 457, 491, 504, 508, 521, 547, 557, 569, 598, 613, 641, 653, 659, 673, 683, 700, 719, 733, 739

Offset: 1

Author

Juri-Stepan Gerasimov, Oct 29 2010, Oct 31 2010

Keywords

• nonn

Comments

(Number of primes of the form n-2^k) = (number of primes of the form n-2^k+1).

Examples

			a(2)=6 because A109925(6) = A109925(7) = 2.
		

Links

• Muniru A Asiru, Table of n, a(n) for n = 1..332

Crossrefs

Cf. A000040, A000079.

Programs

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

Maple

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:
isA175956 := proc(n) A109925(n) = A109925(n+1) ; end proc:
for n from 1 to 1500 do if isA175956(n) then printf("%d,",n); end if; end do:
# R. J. Mathar, Oct 30 2010

Mathematica

SequencePosition[Table[Count[n-2^Range[0,Floor[Log2[n]]],?PrimeQ],{n,800}],{x,x_}][[;;,1]] (* Harvey P. Dale, Oct 21 2024 *)

Formula

A109925(a(n)) = A109925(a(n) + 1).

Extensions

More terms from Klaus Brockhaus and R. J. Mathar, Oct 30 2010