In Word Ways, way back when in May 1970, Kickshaws introduced the problem of a 1-2-3-4-5 Pyramid Word. This is a word having a letter pattern such that there is one of one letter, two of a second letter, etc., up to five of a fifth letter.
Brang, Pamela H.
"A Fifteen-Letter Pyramid,"
Word Ways: Vol. 5
, Article 15.
Available at: http://digitalcommons.butler.edu/wordways/vol5/iss4/15