This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A249730 #19 Feb 20 2022 20:26:22 %S A249730 1,9,15,25,35,49,77,121,143,147,153,169,221,289,323,361,437,529,667, %T A249730 841,899,961,1147,1369,1517,1681,1763,1849,2021,2209,2491,2809,3127, %U A249730 3481,3599 %N A249730 Odd nonprime terms in A250251. %C A249730 This sequence lists the numbers which together with all their multiples with the powers of 2 give the starting values for the prime recurrences whose union is A250251, the fixed points of permutations A250249 and A250250. %C A249730 After 1, contains the terms from columns 2 and 3 of the Sieve of Eratosthenes: A083140 (A083221), but only from those rows r for which A055396(r) (the index of smallest dividing prime r) is fixed by A250249 and A250250, i.e., is in A250251. The first r for which this is not the case is 73, which is in A249729 instead. However, because there are infinitely many primes in A250251, and especially because 2 and 3 are among them, this sequence is infinite. %o A249730 (Scheme, with _Antti Karttunen_'s IntSeq-library) %o A249730 (define A249730 (MATCHING-POS 1 1 (lambda (n) (and (odd? n) (not (prime? n)) (= n (A250249 n)))))) %Y A249730 Subsequence of A250251. %Y A249730 Cf. A083140, A083221, A249821, A250249, A250250. %K A249730 nonn %O A249730 1,2 %A A249730 _Antti Karttunen_, Nov 18 2014