A088108 a(1)=1, a(n) = least odd triangular number which is a proper multiple of a(n-1).

1, 3, 15, 45, 1035, 85905, 1116765, 657774585, 16566052923225, 1679075536205721159675, 5080495373624679083985366566435450475, 61777199356706369989502028371103145170633166772200816412636015025

Offset

1,2

Links

Table of n, a(n) for n=1..12.

Prog

(PARI) my(v=[1, 3, 15, 45, 1035]); for (i=1, #v, print1(v[i], ", ")); n = 1035; for (j = 1, 8, f = factor(n); m = matsize(f)[1]; a = vector(2^m); count = 0; moz = vector(m, x, [ -1, 0]); forvec(x = moz, count++; r = chinese(Mod(x[1], f[1, 1]^f[1, 2]), Mod(x[2], f[2, 1]^f[2, 2])); for (i = 3, m, r = chinese(r, Mod(x[i], f[i, 1]^f[i, 2]))); a[count] = lift(r)); a = vecsort(a); b = vector(2^m, i, a[i]*(a[i] + 1)/2); i = 3; while (!(b[i]%2), i++); n = b[i]; print1(n, ", ")); \\ David Wasserman, Jul 20 2005

Crossrefs

Cf. A014493 (odd triangular numbers).

Sequence in context: A110464 A261505 A331505 * A226030 A232077 A163383

Adjacent sequences: A088105 A088106 A088107 * A088109 A088110 A088111

Keyword

nonn

Author

Amarnath Murthy, Sep 24 2003

Extensions

More terms from Mark Hudson (mrmarkhudson(AT)hotmail.com), Aug 25 2004

3 more terms from David Wasserman, Jul 20 2005

Status

approved