A074238 Numbers n such that the sum of the reverses of 1,2,...,n is a perfect square.

1, 8, 26, 53, 3087, 6173, 8091, 12330, 18358, 42898, 294847, 27382381, 49290155, 426131190, 1350661780, 3161620702, 4461944219, 17625479383, 40766706170, 61554358125, 270930998357

Offset

1,2

Comments

a(22) > 5*10^11. - Giovanni Resta, Apr 16 2017

Links

Table of n, a(n) for n=1..21.

Example

reverse(1) + reverse(2) + ... + reverse(25) + reverse(26) = 1 + 2 + ...+ 52 + 62 = 729 = 27^2, so 26 is a term of the sequence.

Mathematica

s = 0; r = {}; For[i = 1, i <= 10^5, i++, s = s + FromDigits[Reverse[IntegerDigits[i]]]; If[IntegerQ[s^(1/2)], r = Append[r, i]]]; r

Crossrefs

Cf. A062918.

Sequence in context: A143894 A126176 A240754 * A126264 A347677 A225274

Adjacent sequences: A074235 A074236 A074237 * A074239 A074240 A074241

Keyword

base,nonn

Author

Joseph L. Pe, Sep 19 2002

Extensions

a(11)-a(21) from Giovanni Resta, Apr 16 2017

Status

approved