A117978 Triangular numbers with only even digits.

0, 6, 28, 66, 406, 666, 820, 2080, 2628, 8646, 28680, 42486, 48828, 64620, 66066, 80200, 84666, 200028, 204480, 228826, 264628, 288420, 426426, 446040, 468028, 484620, 600060, 626640, 644680, 686206, 828828, 886446, 2222886, 2248260, 2862028, 2888406

Offset: 1

Author

Luc Stevens (lms022(AT)yahoo.com), May 03 2006

Keywords

• base
• nonn
• changed

Comments

There are infinitely many terms. For example all 88...88 6 44...44 6 with an equal number of 8's and 4's (their triangular indices being A185127). - Shyam Sunder Gupta, Aug 16 2025

Links

• Jon E. Schoenfield, Table of n, a(n) for n = 1..10000 (first 1000 terms from Harvey P. Dale)
• Shyam Sunder Gupta, Triangular Numbers, Exploring the Beauty of Fascinating Numbers, Springer (2025) Ch. 3, 82-125.

Crossrefs

Intersection of A000217 and A014263.

Cf. A117960, A185127.

Programs

Mathematica

Select[Accumulate[Range[0,5000]],Count[IntegerDigits[#],?(OddQ)] ==0&] (* _Harvey P. Dale, Oct 21 2011 *)

Extensions

Corrected (a(32) was in error) and extended by Harvey P. Dale, Oct 21 2011