A123722 - OEIS

A123722

Values of n for which A000224(n)=Ceiling[(n+1)/3]; A000224(n) is the number of squares mod n.

1, 3, 4, 8, 9, 15, 21, 33, 35, 39, 51, 57, 69, 70, 87, 93, 111, 123, 129, 141, 159, 177, 183, 201, 213, 219, 237, 249, 267, 291, 303, 309, 321, 327, 339, 381, 393, 411, 417, 447, 453, 471, 489, 501, 519, 537, 543, 573, 579, 591, 597, 633, 669, 681, 687, 699, 717

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OFFSET

1,2

COMMENTS

Conjecture. If n>2 and a(n) is a multiple of 3, then a(n)/3 is a prime; further, all odd primes are given as a(n)/3 for some n. (This has been verified up to n=2000.)

LINKS

Table of n, a(n) for n=1..57.

CROSSREFS

Cf. A000224, A123723.

Sequence in context: A135276 A058074 A319875 * A328733 A217788 A273257

Adjacent sequences: A123719 A123720 A123721 * A123723 A123724 A123725

KEYWORD

nonn

AUTHOR

John W. Layman, Oct 09 2006

STATUS

approved