A077759 Smaller of the two successive triangular numbers which differ in the use of only one digit.

0, 1, 3, 10, 15, 21, 45, 105, 136, 190, 210, 231, 325, 435, 465, 780, 1081, 1225, 1485, 1596, 2415, 3081, 4005, 4465, 4560, 5253, 6670, 7021, 7750, 9730, 14365, 15576, 16653, 17020, 19306, 20100, 20301, 23436, 24310, 24531, 30135, 30628, 36585

Offset

1,3

Comments

The i-th triangular number T(i) is in the sequence if and only if its successor T(i+1) can be obtained by changing a single digit of T(i) and, if necessary, changing the order of the digits. Thus the sequence does not include 55, even though it and its successor 66 could be said to "differ in the use of only one digit" (i.e., using 5 vs. using 6). Triangular numbers such as 404550, whose successor 405450 uses the same digits in the same frequencies, would also be excluded. - Jon E. Schoenfield, Sep 05 2009

Links

Table of n, a(n) for n=1..43.

Example

231 belongs to this sequence as 231 and 253 differ in the use of only one digit, i.e., 1 and 5.

Crossrefs

Sequence in context: A108770 A112355 A074314 * A278291 A247420 A063231

Adjacent sequences: A077756 A077757 A077758 * A077760 A077761 A077762

Keyword

base,nonn

Author

Amarnath Murthy, Nov 21 2002

Extensions

More terms from Jon E. Schoenfield, Sep 05 2009

Status

approved