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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

Table of n, a(n) for n=1..63.

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.)