OFFSET
1,2
COMMENTS
For k = 1..5, let M_k be the set of lattice points with a value equal to k mod 5; the sets M_1, ..., M_5 form 5 arms that spiral around the origin (see representation in Links section). As a consequence, the sequence alternates runs of terms in arithmetic progression with first difference 5.
This sequence appears to be a permutation of the natural numbers.
This sequence has similarities with A308505.
LINKS
Rémy Sigrist, Table of n, a(n) for n = 1..10201
Rémy Sigrist, Colored representation of the spiral for 500 <= x <= 500 and 500 <= y <= 500 (where the color is function of a(n) mod 5)
Rémy Sigrist, Colored scatterplot of (n, a(n)n) for n = 1..40401 (where the color is function of a(n) mod 5)
Rémy Sigrist, PARI program for A308776
EXAMPLE
The spiral begins:
898479746964123118113108103
 
94 544944393478736863 98
   
99 59 29241914433833 58 93
     
95 55 25 151091813 28 53 88
       
100 60 30 20 543 8 23 48 83
         
105 65 35 21 6 12 17 42 77 112
        
110 70 40 26 1116712 37 72 107
      
115 75 45 313641222732 67 102
    
120 80 5046515647525762 97
  
125 85906166717681828792

130135140869196101106111116117
PROG
(PARI) See Links section.
CROSSREFS
KEYWORD
nonn
AUTHOR
Rémy Sigrist, Jun 24 2019
STATUS
approved