A078274 a(n) is the number from which if odd-positioned digits are deleted then one gets the concatenation of first n odd numbers, while if even-positioned digits are deleted then one gets reverse concatenation of first n odd numbers. Position of least significant digit is considered to be 1.

11, 1331, 153351, 17355371, 1937557391, 11315977951311, 113351719917151331, 1135517391111917351351, 11375175911311113917551371, 113951779115111331115917751391, 1231517991171115311351117917952311, 12335271911911173115511371119927152331

Offset

1,1

Comments

a(n) is formed by interleaving the digits of A019519(n) and A038395(n). - Sean A. Irvine, Jun 26 2025

Links

Table of n, a(n) for n=1..12.

Example

a(4) = 17355371: deleting alternate digits starting from the LSD gives 1357. Deleting the other digits gives 7531.

Prog

(PARI) a(n) = {my(d, v=w=[1]); for(i=2, n, v=concat(v, d=digits(2*i-1)); w=concat(d, w)); fromdigits(vector(2*#v, i, if(i%2, v[1+i\2], w[i/2]))); } \\ Sean A. Irvine, Jun 26 2025

Crossrefs

Cf. A078275, A078276, A078277, A078278.

Cf. A019519, A038395.

Sequence in context: A223039 A161586 A209093 * A013716 A110195 A015484

Adjacent sequences: A078271 A078272 A078273 * A078275 A078276 A078277

Keyword

base,nonn

Author

Amarnath Murthy, Nov 25 2002

Extensions

More terms from Antonio G. Astudillo (afg_astudillo(AT)lycos.com), Apr 19 2003

Corrected and extended by Harvey P. Dale, Apr 11 2012

Original terms restored by Sean A. Irvine, Jun 26 2025

Status

approved