A240754 Numbers k with digit_sum(k*k) - 1 = digit_sum((k+1)*(k+1)).

8, 26, 53, 98, 107, 143, 161, 170, 179, 188, 224, 233, 242, 260, 269, 278, 287, 296, 350, 368, 386, 404, 413, 431, 449, 476, 494, 503, 539, 548, 557, 584, 593, 629, 638, 647, 674, 683, 737, 746, 773, 791, 818, 827, 863, 872, 908, 926, 944, 998, 1007, 1043

Offset: 1

Author

Reinhard Zumkeller, Apr 12 2014

Keywords

• nonn
• base

Comments

A240752(a(n)) = 0.

Links

• Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A202089, A239878, A004159, A007953, A000290.

Programs

Haskell

import Data.List (elemIndices)
a240754 n = a240754_list !! (n-1)
a240754_list = elemIndices (-1) a240752_list

Python

def ds(n): return sum(map(int, str(n)))
def ok(n): return ds(n*n) - 1 == ds((n+1)*(n+1))
print(list(filter(ok, range(1044)))) # Michael S. Branicky, Aug 26 2021