VOOZH about

URL: https://oeis.org/A391243

⇱ A391243 - OEIS

login
A391243
Odd numbers k such that Stern polynomial B(k,x) can be expressed as a product of two Stern polynomials B(i,x) and B(j,x), with i,j < k.
5
9, 27, 35, 39, 45, 49, 69, 105, 119, 135, 153, 177, 187, 195, 219, 221, 225, 237, 275, 279, 285, 297, 315, 355, 365, 371, 399, 423, 429, 437, 441, 495, 527, 549, 615, 729, 759, 775, 777, 837, 873, 891, 899, 923, 945, 957, 961, 1107, 1113, 1125, 1221, 1257, 1385, 1431, 1449, 1611, 1675, 1689, 1691, 1755, 1911, 2015
OFFSET
1,1
LINKS
FORMULA
{odd k such that A391239(k) > 2}.
EXAMPLE
See the last two examples in A391242.
PROG
(PARI) is_A391243(n) = (n%2 && 2<sumdiv(n, d, A391260_sq(d, n/d)==n));
CROSSREFS
Cf. A391239.
Odd terms of A391242. Odd numbers that occur more than twice in square array A391260.
Subsequence of A389917.
Subsequences: A060867\{1}, A391256 (semiprimes present).
Cf. A125184, A260443 for a description of Stern polynomials.
Sequence in context: A340237 A216168 A036303 * A390051 A359030 A325299
KEYWORD
nonn
AUTHOR
Antti Karttunen, Dec 06 2025
STATUS
approved