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 A267894 Numbers whose number of odd divisors is nonprime. 1
 1, 2, 4, 8, 15, 16, 21, 27, 30, 32, 33, 35, 39, 42, 45, 51, 54, 55, 57, 60, 63, 64, 65, 66, 69, 70, 75, 77, 78, 84, 85, 87, 90, 91, 93, 95, 99, 102, 105, 108, 110, 111, 114, 115, 117, 119, 120, 123, 125, 126, 128, 129, 130, 132, 133, 135, 138, 140, 141, 143, 145, 147, 150 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS EXAMPLE The divisors of 42 are 1, 2, 3, 6, 7, 14, 21, 42. The odd divisors of 42 are 1, 3, 7, 21. There are 4 odd divisors of 42 and 4 is a nonprime number, so 42 is in the sequence. PROG (PARI) isok(n) = ! isprime(sumdiv(n, d, (d%2))); \\ Michel Marcus, Apr 04 2016 CROSSREFS Cf. A000079, A001227, A018252, A028982, A028983, A131651, A230577, A266531, A267891, A267892, A267893, A267895. Sequence in context: A097100 A002954 A019278 * A084345 A084561 A277166 Adjacent sequences:  A267891 A267892 A267893 * A267895 A267896 A267897 KEYWORD nonn AUTHOR Omar E. Pol, Apr 04 2016 STATUS approved

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Last modified September 29 07:27 EDT 2020. Contains 337425 sequences. (Running on oeis4.)