A080472 a(n) = smallest triangular number that is obtained by placing digits anywhere in n; a(n) = n if n is a triangular number.

1, 21, 3, 45, 15, 6, 78, 28, 91, 10, 171, 120, 136, 1431, 15, 136, 171, 1081, 190, 120, 21, 1225, 231, 2145, 253, 276, 276, 28, 2926, 300, 231, 325, 3003, 2346, 325, 36, 378, 378, 3916, 406, 741, 4278, 435, 4465, 45, 406, 4278, 1485, 496, 1540, 351, 528, 153, 1540

Offset

1,2

Links

Michael S. Branicky, Table of n, a(n) for n = 1..10000

Prog

(Python)
from math import isqrt
from itertools import count
def dmo(n, t):
    if t < n: return False
    while n and t:
        if n%10 == t%10:
            n //= 10
        t //= 10
    return n == 0
def a(n):
    return next(t for t in (i*(i+1)//2 for i in count(isqrt(2*n))) if dmo(n, t))
print([a(n) for n in range(1, 77)]) # Michael S. Branicky, Jan 21 2023

Crossrefs

Cf. A068164, A068165, A080470, A080471.

Sequence in context: A218249 A040433 A317321 * A118389 A077690 A018855

Adjacent sequences: A080469 A080470 A080471 * A080473 A080474 A080475

Keyword

base,nonn

Author

Amarnath Murthy, Mar 07 2003

Extensions

More terms from Ray Chandler, Oct 11 2003

Status

approved