A028839 Sum of digits of n is a square.

1, 4, 9, 10, 13, 18, 22, 27, 31, 36, 40, 45, 54, 63, 72, 79, 81, 88, 90, 97, 100, 103, 108, 112, 117, 121, 126, 130, 135, 144, 153, 162, 169, 171, 178, 180, 187, 196, 202, 207, 211, 216, 220, 225, 234, 243, 252, 259, 261, 268, 270, 277, 286, 295, 301, 306, 310

Offset: 1

Author

N. J. A. Sloane

Keywords

• nonn
• base
• easy

Comments

Difference between two consecutive terms is never equal to 8. - Carmine Suriano, Mar 31 2014

In this sequence, there is no number of the form 3*k-1. In other words, if a(n) is not divisible by 9, it must be of the form 3*k+1. - Altug Alkan, Apr 08 2016

Examples

			234511 belongs to the sequence as its sum of digits is 16, a square.
		

Links

• Carmine Suriano, Table of n, a(n) for n = 1..1242

Crossrefs

Cf. A007953, A028837, A050626.

Cf. A053057 (squares whose digit sum is also a square).

Programs

Magma

[n: n in [1..400] | IsSquare(&+Intseq(n))];  // Bruno Berselli, May 26 2011

Mathematica

Select[ Range[ 500 ], IntegerQ[ Sqrt[ Apply[ Plus, IntegerDigits[ # ] ] ] ]& ]

PARI

isok(n) = issquare(sumdigits(n)); \\ Michel Marcus, Oct 30 2014

Extensions

More terms from Erich Friedman