A145043 Primes p for which s=2 is the least positive integer such that sp-t(sp) is a triangular number, where t(n) is the maximal triangular number not exceeding n.
5, 17, 23, 47, 53, 71, 73, 127, 173, 233, 251, 269, 281, 347, 353, 359, 431, 487, 491, 509, 541, 563, 569, 593, 613, 677, 743, 773, 827, 857, 863, 883, 929, 953, 977, 1013, 1153, 1187, 1283, 1319, 1361, 1373, 1439, 1481, 1583, 1613, 1619, 1709, 1871, 1997
Offset: 1
Keywords
Programs
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PARI
maxt(n) = {k = 1; while ((t=k*(k+1)/2) < n, k++); if (t == n, t, k--; k*(k+1)/2);} lista(nn) = {forprime(p = 2, nn, if (! ispolygonal(p - maxt(p), 3) && ispolygonal(2*p - maxt(2*p), 3), print1(p, ", ");););} \\ Michel Marcus, Jul 25 2014
Extensions
More terms from Michel Marcus, Jul 25 2014