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A092944 Group the natural numbers so that the n-th group contains n numbers whose sum as well as the group product + 1 is prime. Sequence contains the first member of the groups. 3
2, 1, 3, 5, 11, 15, 20, 27, 36, 44, 54, 64, 76, 89, 102, 117, 132, 149, 166, 184, 204, 228, 249, 272, 296, 323, 349, 376, 403, 432, 461, 493, 524, 556, 589, 625, 660, 697, 737, 775, 814, 855, 898, 943, 987, 1031, 1076, 1122, 1169, 1219, 1269, 1321, 1373, 1427 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

1,1

COMMENTS

The n-th group is chosen so that it is lexicographically earliest.

First n-2 numbers are the least previously unused numbers.

The (n-1)st number is chosen with the additional condition that if the product is odd, the sum is also odd (to avoid an impossible situation in picking the n-th number).

The n-th number is chosen as the least unused number that meets the two prime conditions.

In the 3rd group, 6 is selected as the 2nd number rather than 5, else no 3rd number could be found to meet the prime conditions.

LINKS

Table of n, a(n) for n=1..54.

EXAMPLE

Table begins:

2

1,4

3,6,10

5,7,8,9

11,12,13,14,23

15,16,17,18,19,28

CROSSREFS

Cf. A092945, A092946, A092947.

Sequence in context: A169912 A316994 A316993 * A049902 A096631 A144057

Adjacent sequences:  A092941 A092942 A092943 * A092945 A092946 A092947

KEYWORD

nonn,tabl

AUTHOR

Amarnath Murthy, Mar 23 2004

EXTENSIONS

Edited and extended by Ray Chandler, May 07 2008

STATUS

approved

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Last modified January 17 23:15 EST 2019. Contains 319251 sequences. (Running on oeis4.)