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 A257689 Numbers that are either ludic or prime. 4
 1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 25, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 77, 79, 83, 89, 91, 97, 101, 103, 107, 109, 113, 115, 119, 121, 127, 131, 137, 139, 143, 149, 151, 157, 161, 163, 167, 173, 175, 179, 181, 191, 193, 197, 199, 209, 211, 221, 223, 227, 229, 233, 235, 239, 241, 247, 251, 257, 263, 265 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Antti Karttunen, Table of n, a(n) for n = 1..10181 PROG (Scheme, with Antti Karttunen's IntSeq-library) (define A257689 (MATCHING-POS 1 1 (lambda (n) (or (= 1 (A192490 n)) (= 1 (A010051 n)))))) CROSSREFS Union of primes (A000040) and ludic numbers (A003309). Cf. A192506 (complement, neither ludic nor prime), A192503 (ludic and prime), A192504 (ludic and nonprime), A192505 (nonludic and prime). Differs from A206074(n-1), A186891(n) and A257688(n) for the first time at n=19, where a(19) = 59, while A206074(18) = A186891(19) = A257688(19) = 55, a term missing from here. Differs from A257691 for the first time at n=24, where a(24) = 77, while A257691(24) = 79. Sequence in context: A206074 A325559 A257688 * A257691 A164574 A079603 Adjacent sequences:  A257686 A257687 A257688 * A257690 A257691 A257692 KEYWORD nonn AUTHOR Antti Karttunen, May 07 2015 STATUS approved

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Last modified April 9 06:59 EDT 2020. Contains 333344 sequences. (Running on oeis4.)