A293518 Number of surviving even nodes at generation n in the binary tree of persistently squarefree numbers (see A293230).

0, 1, 1, 2, 2, 2, 3, 6, 6, 8, 12, 16, 20, 31, 34, 56, 63, 88, 112, 150, 208, 287, 379, 511, 690, 908, 1239, 1637, 2252, 2945, 4052, 5348, 7203, 9681, 12974, 17432, 23470, 31419, 42254, 57026, 76182, 102845, 137764, 185271, 249065, 334864, 449586, 604164, 811709, 1089661, 1465433, 1968592

Offset

0,4

Links

Table of n, a(n) for n=0..51.

Formula

a(n) = Sum_{k=(2^n)..(2^(1+n))-1)] abs(A293233(k)) * [0==(A008966(2k)] * [1==A008966(1+2k))].

a(n) + A293519(n) = A293521(n).

a(n) - A293519(n) = A293517(n).

Example

a(3) = 2 because in the binary tree illustrated in A293230, there are two even nodes at the level 3 (namely, the nodes 10 and 14) that spawn just one offspring each.

Prog

(PARI)
\\ Compute the sequences A293441, A293518 and A293519 at the same time:
allocatemem(2^30);
next_living_bud_or_zero(n) = if(issquarefree(n), n, 0);
nextA293230generation(tops) = { my(new_tops = vecsort(vector(2*#tops, i, next_living_bud_or_zero((2*tops[(i+1)\2])+((i+1)%2))), , 8)); if(0==new_tops[1], vector(#new_tops-1, i, new_tops[1+i]), new_tops); }
writeA293441etc_counts(n, tops) = { my(os=0, es=0, k=0); for(i=1, #tops, if((tops[i]%2), k++; if(!issquarefree(1+(2*tops[i])), os++), if(issquarefree(1+(2*tops[i])), es++)); ); write("b293441.txt", n, " ", k); write("b293518.txt", n, " ", es); write("b293519.txt", n, " ", os); print1(k, ", "); }
tops_of_tree = [1];
write("b293441.txt", 0, " ", 1);
write("b293518.txt", 0, " ", 0);
write("b293519.txt", 0, " ", 0);
print1(1, ", ");
for(n=1, 51, tops_of_tree = nextA293230generation(tops_of_tree); writeA293441etc_counts(n, tops_of_tree); );
(Scheme)
(define (A293518 n) (add (lambda (k) (* (if (and (= 0 (A008966 (+ k k))) (= 1 (A008966 (+ 1 k k)))) 1 0) (abs (A293233 k)))) (A000079 n) (+ -1 (A000079 (+ 1 n)))))
;; Implements sum_{i=lowlim..uplim} intfun(i)
(define (add intfun lowlim uplim) (let sumloop ((i lowlim) (res 0)) (cond ((> i uplim) res) (else (sumloop (1+ i) (+ res (intfun i)))))))

Crossrefs

Cf. A008966, A293230, A293233, A293517, A293519, A293521.

Sequence in context: A306393 A324763 A038715 * A057040 A363772 A096235

Adjacent sequences: A293515 A293516 A293517 * A293519 A293520 A293521

Keyword

nonn

Author

Antti Karttunen, Oct 16 2017

Status

approved