A161720 a(n) = (prime(n) - 7)/2.

-1, 0, 2, 3, 5, 6, 8, 11, 12, 15, 17, 18, 20, 23, 26, 27, 30, 32, 33, 36, 38, 41, 45, 47, 48, 50, 51, 53, 60, 62, 65, 66, 71, 72, 75, 78, 80, 83, 86, 87, 92, 93, 95, 96, 102, 108, 110, 111, 113, 116, 117, 122, 125, 128, 131, 132

Offset: 3

Author

G. A. Isa (isaabor(AT)yahoo.com), Jun 18 2009

Keywords

• sign
• easy
• less

Comments

Original name was: Half the difference between the first and the last numbers in the 7th circle of the cyclic representation of some structures whose cardinality generates Aminu numbers.

A bijective operator is defined on the Aminu numbers which in turn generates another cyclic group. Aminu numbers were first reported as the cardinality of some subgroups of regular groups whose order and degree coincide (Ibrahim,2004;2005;2007 and Ibrahim and Audu 2005). The action of the operator on the group structures where constructed using some special succession scheme which led to sequences such as A005097. This sequence enumerates half the difference between the first and last numbers in the 7th cycle of such group structures.

Examples

			For Pn=5, a(1)=-2/2=-1, for Pn=7, a(2)=0/2=0, for Pn=11,a(3)=4/2=2
		

References

• A. A. Ibrahim, Group theoretic interpretation of Bara'a al-Dhimmah Models: Proceedings of Annual National Conference of Mathematical Association of Nigeria, MAN,(2004), 35-40.
• A. A. Ibrahim and M. S. Audu, Some Group Theoretic Properties of Certain class of (123) and (132)- Avoiding Patterns of numbers: An enumeration scheme,African Journal of Natural Sciences, 8(1)(2005), 79-84.
• A. A. Ibrahim, An Enumeration scheme and Algebraic properties of a special (132)- avoiding class of permutations Patterns, Trends in Applied sciences Research, Academic Journal Inc. 2(4)(2007), 334-340.

Crossrefs

Cf. A178674, A000040, A005097.

Essentially a duplicate of A105760.

Programs

PARI

a(n)=(prime(n)-7)/2 \\ Charles R Greathouse IV, Jun 15 2013

Formula

a(n) = A105760(n-3). - R. J. Mathar, Sep 11 2012

Extensions

Name changed by Arkadiusz Wesolowski, Jun 15 2013