A035253 - OEIS

A035253

Second differences are 2,2,1,2,1,1,2,1,1,1,2,1,1,1,1,2,1,1,1,1,1,2,.. (A035214).

4, 1, 0, 1, 3, 7, 12, 18, 26, 35, 45, 56, 69, 83, 98, 114, 131, 150, 170, 191, 213, 236, 260, 286, 313, 341, 370, 400, 431, 463, 497, 532, 568, 605, 643, 682, 722, 763, 806, 850, 895, 941, 988, 1036, 1085, 1135, 1186, 1239, 1293, 1348, 1404, 1461, 1519, 1578

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OFFSET

0,1

LINKS

Table of n, a(n) for n=0..53.

FORMULA

a(n) = A060432(n-1)+4+n*(n-7)/2. - Chai Wah Wu, Jun 07 2025

PROG

(Python)

from math import isqrt

def A035253(n): return (k:=(r:=isqrt(m:=n<<1))+int((m<<2)>(r<<2)*(r+1)+1)-1)*(k*(-k-3)+6*n-8)//6+(n*(n-5)>>1)+3 # Chai Wah Wu, Jun 07 2025

CROSSREFS

Different from A005228. Cf. A035254, A060432.

Sequence in context: A347618 A290459 A290458 * A070432 A170989 A290457

Adjacent sequences: A035250 A035251 A035252 * A035254 A035255 A035256

KEYWORD

nonn,easy

AUTHOR

Robet Bronson (bob(AT)bronsons.com)

EXTENSIONS

More terms from Chai Wah Wu, Jun 07 2025

STATUS

approved