A176693 Union of squares and the even numbers.

0, 1, 2, 4, 6, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 25, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, 49, 50, 52, 54, 56, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78, 80, 81, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104, 106, 108, 110, 112, 114, 116, 118, 120, 121, 122

Offset

1,3

Comments

Numbers k such that k^k is a square. - Chai Wah Wu, Sep 18 2024

Links

Table of n, a(n) for n=1..68.

Mathematica

With[{upto=150}, Union[Join[Range[0, upto, 2], Range[Sqrt[upto]]^2]]] (* Harvey P. Dale, Apr 29 2015 *)

Prog

(PARI) is_A176693(n)=!bittest(n, 0)||issquare(n) \\ M. F. Hasler, Apr 19 2015
(Python)
from math import isqrt
def A176693(n):
    def f(x): return n-1+(x>>1)+(x&1)-(isqrt(x)+1>>1)
    m, k = n-1, f(n-1)
    while m != k: m, k = k, f(k)
    return m # Chai Wah Wu, Sep 18 2024

Crossrefs

Cf. A128201 (Union of squares and the odd numbers).

Sequence in context: A247423 A182339 A110262 * A352872 A118672 A100417

Adjacent sequences: A176690 A176691 A176692 * A176694 A176695 A176696

Keyword

nonn,easy

Author

Vincenzo Librandi, Apr 24 2010

Extensions

Initial a(1)=0 added by M. F. Hasler, Apr 20 2015

Status

approved