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A131651 Positive integers obtained as the difference of two triangular numbers in exactly 4 ways. 0
15, 21, 27, 30, 33, 35, 39, 42, 51, 54, 55, 57, 60, 65, 66, 69, 70, 77, 78, 84, 85, 87, 91, 93, 95, 102, 108, 110, 111, 114, 115, 119, 120, 123, 125, 129, 130, 132, 133, 138, 140, 141, 143, 145, 154, 155, 156, 159, 161, 168, 170, 174, 177, 182, 183, 185, 186, 187 (list; graph; refs; listen; history; internal format)
OFFSET

1,1

COMMENTS

It appears that terms of the sequence are all given by a power of 2 times the cube of an odd prime or a power of 2 times a product of two distinct odd primes. (This has been verified for a(n)<=10000.)

CROSSREFS

Cf. A001227, A038550, A072502.

Sequence in context: A057489 A070811 A138594 * A134642 A072974 A082686

Adjacent sequences:  A131648 A131649 A131650 * A131652 A131653 A131654

KEYWORD

nonn

AUTHOR

John W. Layman (layman(AT)math.vt.edu), Sep 10 2007

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Last modified February 15 13:48 EST 2012. Contains 205810 sequences.