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A072864 Numbers n such that the smallest k dividing sigma(k*n^2) is equal to 3. 1
7, 13, 14, 19, 21, 26, 28, 31, 35, 37, 38, 39, 42, 43, 52, 56, 57, 61, 62, 63, 65, 67, 70, 73, 74, 76, 77, 78, 79, 84, 86, 91, 93, 95, 97, 103, 104, 105, 109, 111, 112, 114, 117, 119, 122, 124, 126, 127, 129, 130, 133, 134, 139, 140, 143, 146, 148, 151, 152, 154 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

Sequence contains primes of the form 6x+1 (A002476) and multiples of those primes, except (6x+1)^2. If x is not in the sequence, the smallest k dividing sigma(k*x^2) is equal to 6.

LINKS

Table of n, a(n) for n=1..60.

PROG

(PARI) isok(n) = A049605(n^2) != 6; \\ Michel Marcus, Nov 21 2013

CROSSREFS

Cf. A049605.

Sequence in context: A233593 A013651 A050931 * A232437 A275201 A274558

Adjacent sequences:  A072861 A072862 A072863 * A072865 A072866 A072867

KEYWORD

easy,nonn

AUTHOR

Benoit Cloitre, Jul 27 2002

STATUS

approved

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Last modified October 14 23:54 EDT 2019. Contains 328025 sequences. (Running on oeis4.)