A307034 a(n) is the smallest integer k of the form k = x*(x + a(n-1)), such that A324920(k) = n, for some positive integer x, with a(0) = 0.

0, 1, 2, 3, 10, 11, 26, 87, 178, 179, 362, 1835, 22164, 155197, 620804, 5587317, 55873270, 167619819, 1340958616, 57661222337, 345967334058, 25255615391563, 858690923314298, 4293454616571515, 60108364632001406, 3185743325496077327, 178401626227780333448, 1605614636050023001113

Offset: 0

Author

Daniel Suteu and Robert G. Wilson v, Mar 23 2019

Keywords

• nonn

Comments

Inspired by A324921.

This sequence provides upper bounds for A324921, i.e.: A324921(n) <= a(n).

Crossrefs

Cf. A056737, A324920, A324921.

Programs

PARI

f(n) = my(d=divisors(n)); d[(2+#d)\2]-d[(1+#d)\2]; \\ A056737
g(n) = my(k=0); while(n!=0, k++; n=f(n)); k; \\ A324920
a(n) = if(n <= 0, return(0)); my(t=a(n-1)); for(k=1, oo, if(g(k*(k+t)) == n, return(k*(k+t))));