A080162 Wonderful Demlo numbers A002477 whose digit sums are squares.

1, 121, 12321, 1234321, 123454321, 12345654321, 1234567654321, 123456787654321, 12345678987654321, 12345679012345679012345679012345678987654320987654320987654320987654321

Offset: 1

Author

Eric W. Weisstein, Jan 31 2003

Keywords

• nonn
• base

Comments

The next term (a(11)) has 101 digits. - Harvey P. Dale, Jun 16 2025

Links

• Jeppe Stig Nielsen, Table of n, a(n) for n = 1..23
• Eric Weisstein's World of Mathematics, Demlo Number

Crossrefs

Cf. A080160, A080161, A002477, A080151.

Programs

Mathematica

Select[LinearRecurrence[{111,-1110,1000},{1,121,12321},40],IntegerQ[Sqrt[Total[IntegerDigits[#]]]]&] (* Harvey P. Dale, Jun 16 2025 *)

PARI

for(k=1,100,my(d=((10^k-1)/9)^2); issquare(sumdigits(d)) && print1(d,", ")) \\ Jeppe Stig Nielsen, May 27 2023