A122799 A P_7-stuttered arithmetic progression with a(n+1)=a(n) if n is not a heptagonal number, a(n+1)=a(n)+2 otherwise.

1, 1, 3, 5, 7, 9, 11, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49, 51, 53, 55, 57, 59, 61, 61, 63, 65, 67, 69, 71, 73, 75, 77, 79, 81, 83, 85, 87, 89, 91, 93, 95, 97, 99, 101, 101, 103, 105, 107, 109, 111, 113, 115, 117, 119, 121, 123, 125, 127, 129, 131, 133, 135, 137, 139, 141, 143, 145, 147, 149, 151, 151, 153, 155, 157, 159, 161, 163, 165, 167, 169, 171, 173, 175, 177, 179, 181, 183, 185, 187

Offset: 1

Author

Grady Bullington (bullingt(AT)uwosh.edu), Sep 14 2006

Keywords

• nonn
• easy

Comments

P_7(i) = the i-th heptagonal number.

Links

• Douglas E. Iannucci and Donna Mills-Taylor. On Generalizing the Connell Sequence. Journal of Integer Sequences 2 (1999), Article 99.1.7.
• Grady D. Bullington, The Connell Sum Sequence, J. Integer Seq. 10 (2007), Article 07.2.6. (includes direct formula for a(n))

Crossrefs

Cf. A001614, A122793, A122794, A122795, A122796, A122797, A122798, A122800.

Programs

PARI

isHeptag(n) = {if (! issquare(40*n+9, &res), return (0)); if ((res + 3) % 10, return (0), return (1));}
lista(m) = {aa = 1; for (i=1, m, print1(aa, ", "); if (! isHeptag(i), aa += 2););} \\ Michel Marcus, Apr 01 2013

Formula

a(n) = A045930(n)-n+1.

Extensions

Definition corrected by Michel Marcus, Apr 01 2013