A281006 a(n) = A000203(n) - A052928(n-1).

1, 3, 2, 5, 2, 8, 2, 9, 5, 10, 2, 18, 2, 12, 10, 17, 2, 23, 2, 24, 12, 16, 2, 38, 7, 18, 14, 30, 2, 44, 2, 33, 16, 22, 14, 57, 2, 24, 18, 52, 2, 56, 2, 42, 34, 28, 2, 78, 9, 45, 22, 48, 2, 68, 18, 66, 24, 34, 2, 110, 2, 36, 42, 65, 20, 80, 2, 60, 28, 76, 2, 125, 2, 42, 50, 66, 20, 92, 2, 108, 41, 46, 2, 142, 24, 48, 34, 94, 2

Offset

1,2

Comments

a(n) = 2 iff n is an odd prime (A065091).

Has a symmetric representation as a narrow pyramid with holes, in the same way as A249351.

Links

Antti Karttunen, Table of n, a(n) for n = 1..65537

Index entries for sequences related to sigma(n)

Formula

a(n) = sigma(n) - 2*floor((n - 1)/2) = A000203(n) - 2*A004526(n-1).

a(n) = A048050(n) + A176059(n), n >= 2.

Example

A000203    A052928     a(n)
.   1    -    0    =    1
.   3    -    0    =    3
.   4    -    2    =    2
.   7    -    2    =    5
.   6    -    4    =    2
.  12    -    4    =    8
...

Prog

(PARI) A281006(n) = (sigma(n) - 2*((n-1)>>1)); \\ Antti Karttunen, Sep 25 2018

Crossrefs

Cf. A000203, A004526, A048050, A052928, A065091, A176059, A196020, A235791, A236104, A237048, A237270, A237271, A237591, A237593, A245092, A249351, A262626, A279387, A281010.

Sequence in context: A124219 A103833 A226172 * A046227 A120842 A319044

Adjacent sequences: A281003 A281004 A281005 * A281007 A281008 A281009

Keyword

nonn

Author

Omar E. Pol, Jan 23 2017

Status

approved